The Edain

In the 4th Century FA (First Age) the Edain, drawn towards the Light in the West, entered Beleriand, where many of them entered the services of the Eldar and fought valiantly in the Wars of Beleriand.

-The Complete Guide to Middle-Earth, Robert Foster

Humans are referred to in relation to Elves as the "Second-born", for they arose much later in the history of Arda.

Little is known of the course of events the human folk experienced in their journey from far to the East of Beleriand, where they awoke as the Sunlight of Arien first dawned on Middle-Earth. In the East they had been befriended by Avari and Nandor Elves, from whom they learned some speech and music. The Edain had also dealt, not always in a friendly manner, with Dwarves in the East. But it was not until humans first crossed the Ered Luin mountain range where they would later be met and befriended by Finrod Felagund, that their lives became wound in with the events of Beleriand, where they would settle in various lands.

After arriving in Beleriand from the East, their fortunes would be closely bound with the fate and deeds of the First Age.

The humans known as Edain (or singularly Adan), who are in some places also known as 'Fathers of Men' or 'Elf-friends' were the first to enter Beleriand. They entered in three groups: First came the Beorians, who would later settle in Dorthonion, then the Haladin (who brought with them the Druedain), who after nearly being wiped out by Orcs would follow their leader Lady Haleth to settle in the Forest of Brethil. The Marachians entered Beleriand last. They were the most numerous, and would eventually settle in Dor-Lomin. Many years later, another distinct group, the Easterlings, would find their way into Beleriand, and at first dwell amongst the folk of Feanor's sons.

Taken from Beleriand's help files:
NEWS HUMAN INTRODUCTION.

The Gift of Men

To men was given another fate--which often seems a grievance to them, but which was regarded by Iluvatar as a 'new gift.' This gift is outlined in the Silmarillion as well:

"Therefore he willed that the hearts of Man should seek beyond the world and should find no rest therein; but they should have a virtue to shape their life, amid the powers and chances of the world, beyond the Music of the Ainur.....Death is their fate, the gift of Iluvatar, which as Time wears even the Powers shall envy....(for) Men shall join in the Second music of the Ainur...."

These differences, while making an undeniable distinction between the races, has not kept them from friendships or interaction, and while the Elven kings "set regions apart where Men could live their own lives, and appointed chieftains to hold these lands freely," both Man and Elf ally often in war under their own leaders, and in some cases some of the Edain dwell among the Eldar as long as it is acceptable to the latter--a few even entering into the service under those Elven kings.

Death is the gift given to men by Illuvatar. That Men would age and die, unlike the Eldar (Elves) and would go to the halls of Mandos. From there their fate was unknown and so it was seen as both a blessing and a curse.

Men

Relations

Elves

Elves woke before the sun or moon rose and were known as the Firstborn, created in the image of the Valar. They were the eldest, fairest and noblest of the speaking races of Middle-Earth.
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