help i have no idea how to do/use css

hi hello,,, HELP ME PLZ TT

so uh i tried really realy hard to understand css and apparently i am unable to so,, if anyone sees this..could you maybe give me tips or somthing?? it would be greatly appreciated!!//

...i really wanna make my layout cool but im bit to dum ψ(.. )>ψ(.. )>