How can i remove pending orders from my wallet?

When you go to the checkout page, you can hover over the game you don't want, and a Remove option will appear under the game's name.

There's nothing on the checkout page...just in my orders history are many pending orders with a green button says complete this order

Ignore them and they will eventually disappear on their own after a few hours.

Pending to add money? Or pending to buy a game?

Buying a game should be instant. But the transfer to your wallet may take time, and with the same level of security as say a credit card (not guarenteed but via credit given nearly immediate confirmation and actual transaction within 3 days)