1. initial signs of revelation to the prophet (pbuh)
the initial signs of prophethood were dreams that came true, and that continued for six months, until allah (the almighty) favoured muhammad (pbuh) by prophethood. jibreel, the angel, (pbuh), came to muhammad (pbuh), during his solitude in hira cave, reciting to him the first part of al-alaq surah:
1}read: in the name of your lord who created,
2}created man from clots.
3}read: and your lord is the most honorable,
4}who taught by the pen.
5}he taught man what he did not know.
the belgian intellectual george alfred leon sarton (1884-1956) said:
muhammad (pbuh) declared his message publicly about 610 ac, when he was forty years….just like his brother prophets, (peace be upon them) before him. 
2. the christian scholar and writer waraqah bin nawfal embraced islam
after hearing the first part of al-alaq surah from the prophet pbuh, waraqah said, ”by allah! this is the angel jibreel (pbuh), who was sent to prophet muses (pbuh). i wish i were young when your people would drive you out of makkah!" the prophet (pbuh), wondered: "are they going to drive me out of makkah?" waraqah affirmed positively saying, "never has a man conveyed a message similar to what you have been charged with, except that his people waged enmity against him - if i am to witness this, i will give you unequivocal support.” waraqah then embraced islam. it is a notable record of history that the first man to embrace islam is a christian scholar.
3. the first people to embrace islam
allah (the almighty) commanded his messenger to convey his message secretly for three years. he called his people to islam. early pioneers were his friend and supporter abu-bakr, his wife khadeejah, and his cousin ali-bin-abee-talib, and his servant zaid-bin-haritha (may allah be pleased with all of them).
those were the core element of islam, from which the faith of islam broke forth, and spread everywhere.
ralf linton said: "then the 'revelation' conveyed to muhammad (pbuh) attracted a number of followers, and started spreading among people…".
4. inflicting harm on muslims
when people started to join the faith of allah, one after the other, and the followers of muhammad (pbuh) increased, idolaters started a phase of enmity against them. so, allah (the almighty) protected his messenger (pbuh) by means of the back-up of his uncle abu-talib, who was respected as a noble and a highborn man among his people. as regards new muslims, those who have a tribe sought protection with their tribes, but most of the prophet's followers were attacked severely by idolaters, who did their utmost to extract them away from their new faith. among them was bilal-bin rabah an ethiopian slave, ammar-bin-yasir and his mother somayah, and his household, who were severely tortured, in the cause of allah. ammar-bin-yasir died. abu-jahel passed by somayah, under torture, and killed her by stabbing her in her vulvae.
prominent men of quraish used to torture several women who became muslims . those women set best examples of persistence, patience, and feeling proud of the faith of islam. among them was zoneira, a roman female slave that as a result of converting to islam, was tortured in the cause of allah, until she was hit in her eyes, and became blind. the girl slave of omar-bin moammel (of adey tribe) became a muslim. omar-bin-al-khattab, still in his old days of idolatry, continued hitting her, until he was tired. among women who joined islam and were tortured were om-obeiss, and al-nahdiah, with her daughter.
5. immigration to abyssinia (now ethiopia) and the embracing islam of the king of the abyssinian christians:
the scholar ateen denier spoke of the dilemma of muslims at that time:
"muhammad (pbuh) was filled with sorrow for the great suffering of weak muslims, who were unable to find protection. it was really true courage of those in pains, and of the martyrs in the cause of allah, that proved their steadfast belief in islam. muhammad (pbuh), however, had the view that such a miserable state should not continue. so, he advised the weak muslims, and those who should not necessarily stay in makkah to immigrate to abyssinia, that was a christians country ruled by king an-najashi (negus), who was known for tolerance and justice." 
an-najashi was a righteous christian king, and nobody under his rule was likely to be wronged. muslim immigrants settled as guests for an-najashi at best conditions. when quraish heard of that, they sent a delegation to plot against muslims, and persuade an-najashi to expel muslims out of his land, but that delegation went back disappointed. an-najashi converted to islam after listening to the explicit verses of "mariam surah" of thholy quran receited by jafar-bin-abee-talib (may allah be pleased with him) the head of the muslim immigrants. muslims stayed under the protection of king negus, until they left to (al madina, the first city of islam, at the seventh year from hijra.
6. the siege and the year of sadness
inflicting harm on the messenger of allah (pbuh) (and his followers) became stronger. he, his household, and companions were confined in a mountain col (a col between two mountains in makkah, (similar to a prison in the air) called "shi’b abi-talib". the prophet (pbuh), with his companions, was imprisoned there for three years. hunger and fatigue came to the point that the cries of the children of those under siege were heard from behind the mountain. that siege started in the month of moharam, the tenth year after prophethood, and ended when he was forty nine. a few months later, his uncle abu-talib, who was his main protector, died. then, a short time later, his wife khadeejah (may allah be pleased with her), also died. with that, the disbelievers dared to inflict more injury on the prophet (pbuh) and his companions.
in the month of shawwal, the tenth year from prophethood (end of may, or early july 619 ac) the prophet (pbuh) set out to the city of ta’if, along with (his adoptive son) zaid-bin-haritha (may allah be pleased with him) where he stayed some days, calling to allah (the almighty). the people of ta’if drove him out, and continued their attack by stoning him, until his legs were bleeding. that was the hardest day in his life..
in the month of thul-ke’dah, the tenth year after prophethood (end of may, or early july 619 ac), the prophet (pbuh) came back to resume calling people to islam in makkh once more..
7. calling the tribes to islam, and meeting the people of madienah (called later "al-ansar" or the supporters)
the prophet (pbuh) remained in makkah calling people to the path of allah (the almighty), introd