How to give weapons elemental damage? (Fire, Lightning, Dark)

You won't be able to level up at all until you get past the Things Betwixt area -- essentially, the tutorial. Past that and through a narrow cave is a town called Majula.

When you first enter Majula, there is an area to the right which has a tall tower overlooking the sea. To the right of that, slightly down the cliff and by a tree, there is a green-cloaked woman known as the Emerald Herald. Once you speak to her, she will relocate to the Majula bonfire. Thereafter, you can speak to her and level up at that bonfire. Unlike Dark Souls, this is the only place you can spend souls to level up.

When speaking to her at the Majula bonfire, be sure to wait for a menu to popup. You may have to speak to her several times before the option becomes available.

As a side piece of advice, if you want to save your souls until you can first spend them, don't go down into the area with the two trolls. This is a difficult encounter for a new character. You can bypass that and come back to it later to fight them.

In Dark Souls 1 you could attack from behind shields with spears and rapiers this has been transferred to the second game...

The big change in Dark Souls 2 for weapons of this Nature is the Halberd you can use your Halberd as you would a spear from behind your shield this however changes the type of attack to thrust as apposed to slash so be aware of the enemies resistance to stabbing attacks. As for other Weapons that can be used from behind the shield there are Rapiers and all other types of spear and halberd with a point.

As for your Stamina you can find many ways of increasing the recovery speed such as The Cloranthy Ring and green blossom.