When I open the program it loads, then, when I open a new canvas the program starts to lag and it's impossible to draw anything.
You're probably suffering from a broken display driver. Check https://docs.krita.org/KritaFAQ#Krita_starts_with_a_black_or_blank_canvas_and_nothing_changes_when_you_try_to_draw.2Fshows_a_black_or_blank_screen_on_my_Windows_system_with_an_Intel_GPU
Please tell us the exact brand and model of your computer, the windows version and the display driver version.
*** This bug has been marked as a duplicate of bug 360601 ***