I want to know the size of wire to use to run power to my shed 75' away & the size of breaker;i do have a welder , but I guess it is 120v, just a few lights & small power tools; I was thinking #12 wire & a 20amp breaker would be fine; but I will listen to your advice.. thank-you.

Honestly, I would use #8 wire. You can get #8-3 UF cable. This will help with the welder load, and other misc loads, and future load, and not have any worries.