paint.net is also FREE and there are tutorials and loadsa plug-ins for extra effects, however, I also have GIMP which does much more if you can master all the controls ... a long steep learning curve, but do-able due to the lockdown's enforced leisure time ... my neglected garden is now officially a jungle ( due to West of Scotland more than is necessary rain.)
Here's a crude attempt at colouring in, by numbers, cheers, Ian