Place within the Fellowship

Legolas is one of the Fellowship of the Ring, selected by Elrond to accompany Frodo on his journey:

'The Company of the Ring shall be Nine; and the Nine Walkers shall be set against the Nine Riders that are evil. With you and your faithful servant, Gandalf will go; for this shall be his great task, and maybe the end of his labours.

`For the rest, they shall represent the other Free Peoples of the World: Elves, Dwarves, and Men. Legolas shall be for the Elves; and Gimli son of Glóin for the Dwarves. They are willing to go at least to the passes of the Mountains, and maybe beyond. For men you shall have Aragorn son of Arathorn, for the Ring of Isildur concerns him closely.' -- (from FOTR)

During the journey, Legolas never leads. He takes more of a support role - keeping watch or following at the back to ensure that none fall behind. For instance, when the Fellowship departs from Rivendell:

Gandalf walked in front, and with him went Aragorn, who knew this land even in the dark. The others were in file behind, and Legolas whose eyes were keen was the rearguard. -- (from FOTR)

When sailing the small boats down the Anduin:

The Company was arranged in this way: Aragorn, Frodo, and Sam were in one boat; Boromir, Merry, and Pippin in another; and in the third were Legolas and Gimli, who had now become fast friends. -- (from FOTR)

In the Book of Lost Tales 2, Tolkien describes Legolas as follows:

He (Legolas) was tall as a young tree, lithe, immensely strong, able swiftly to draw a great war-bow and shoot down a Nazgul, endowed with the tremendous vitality of Elvish bodies, so hard and resistant to hurt that he went only in light shoes over rock or through snow, the most tireless of all the Fellowship.

The first reference in The Lord of the Rings is in the chapter named "The Council of Elrond" in the "Fellowship of the Ring".

"There was also a strange Elf clad in green and brown, Legolas,
a messenger from his father, Thranduil, the King of the Elves of Northern Mirkwood. "
-- (from FOTR)

While there is considerable debate about whether Legolas had golden hair or dark hair, as his father King Thranduil had 'golden hair', it's probably safe to assume that Legolas does as well.

Some other descriptions of Legolas:

'Alas! alas!' cried Legolas, and in his fair elvish face there was great distress. -- (from FOTR)

With that he sprang forth nimbly, and then Frodo noticed as if for the first time, though he had long known it, that the Elf had no boots, but wore only light shoes, as he always did, and his feet made little imprint in the snow. -- (from FOTR)

Frodo looked up at the Elf standing tall above him, as he gazed into night, seeking a mark to shoot at. His head was dark, crowned with sharp white stars that glittered in the black pools of the sky behind. -- (from FOTR)

But Legolas stood beside him, shading his bright elven-eyes with his long slender hand, [...]. -- (from TTT)

'Many miles lie between,' said Legolas, gazing thither and shading his eyes with his long hand. -- (from TTT)

Together the Elf and the Dwarf entered Minas Tirith, and folk that saw them pass marvelled to see such companions; for Legolas was fair of face beyond the measure of Men, and he sang an elven-song in a clear voice as he walked in the morning. -- (from ROTK)

The heart of Legolas was running under the stars of a summer night in some northern glade amid the beech-woods; -- (from FOTR)

How Legolas describes himself - if you remember, generally other people introduce Legolas and he rarely speaks to strangers on his own behalf:

'I am one of the Nine Companions who set out with Mithrandir from Imladris, said Legolas and with this Dwarf, my friend, I came with the Lord Aragorn. But now we wish to see our friends. Meriadoc and Peregrin, who are in your keeping, we are told.' -- (from ROTK)

Age

We know that despite his apparently youthful appearance, he is not a young Elf.

'Five hundred times have the red leaves fallen in Mirkwood in my home since then,' said Legolas, 'and but a little while does that seem to us.' -- (from TTT)

In The Two Towers, in describing Fangorn he says:

'It is old, very old,' said the Elf. 'So old that almost I feel young again, as I have not felt since I journeyed with you children. It is old and full of memory. I could have been happy here, if I had come in days of peace.'

In the Two Towers in describing Treebeard the Ent he says

'A legend of Rohan!' cried Legolas. 'Nay, every Elf in Wilderland has sung songs of the old Onodrim and their long sorrow. Yet even among us they are only a memory. If I were to meet one still walking in this world, then indeed I should feel young again! But Treebeard: that is only a rendering of Fangorn into the Common Speech; yet you seem to speak of a person. Who is this Treebeard?'

Weapons

Legolas had a bow and a quiver, and at his belt a long white knife. -- (FOTR)

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