I buit a extracycle, and the chain swings alot and bounches and makes the bike skipm how do I fix it, make it three speed?

Looks like your chain is too long. I would check https://www.parktool.com/repair/readhowto.asp?id=26 before making it a three speed.

I found a way, I put the gear changer on the yellow bike, so now it has two one it and the first one acts like a tentioner, works well.

The bike shop I work at builds a fair number of Extracycles and a certain amount of chain slap seems to be the accepted norm. Skipping is obviously a problem, but there's not a really good way to eliminate all traces of wobble from a three foot long chain line. I'd say go look at some commercially produced Extracycles for comparison, but judging by the picture you've pieced it together almost exactly the same way as they do it. One of the above comments mentions shortening your chain and that might be a good idea. Making the chain a little bit shorter than you normally would seems to get rid of a lot of excessive chain motion. Good luck.