What are the main objectives of uno

The main  objective is to run out of cards.

Explanation:

The game starts by dealing 7 cards to everyone. When someone puts a card the next player has to put a card with the same number or the same color as the last card on the field. There are cards with effects such as: make the next player skip his turn, change the order of putting cards on the field or, make the next player draw 2 cards and skip his turn. If you are don't have the right color or the right number in your hand you can either put one of the black cards (if you have one of them in your hand) which let you change the color on the field (and one of them makes the next player draw 4 cards) or draw one card and skip your turn. When you have 1 card left you have to say "Uno" and when you are out of cards you win.