Hi guys i need help.I always have big problems to make backgrounds in singatures.
Do you have good advices for me?I need big help oO
I wanna make backgrounds like these but i cant

Just start to follow tutorials. It would have helped so much.

Hm , making BG isnt that hard actually .. for the first one he used brushes with light effects that can be done what a normal rounded brush .. i belive he used white vectors then he used adjustment settings to give it colors and blend it. and for the second one its easy , he used 1 C4D or maybe 2 , with space wallpaper and place it on screen or multiply. In general you make BGz with brushes + adjustment settings or with C4D that match with your flow/focal.

usually i use stocks or vectors
try deviant art
or use c4ds/ brushes

Alright dude..
for such signatures, there're two ways to do so..
opening with gradient, getting some VERY HQ c4ds and put it as bg, you need to have good imagination and work a bit on c4d displacement...then use fractals/dodging/burning/soft brushes for effects. then color balance/hue and saturation/curves/photo filters for color adjustments.

or using HQ Game Stock and blurring, embedding a light source, fixing colors and stuff..then adding (fractals/space stocks/bubble c4ds) and using splatter brushes with clip masks for extra cool effects.
Hope i helped, you'd find the best way by experimenting.