I need to make window on a solid wall. I have no idea how to do so. Also i mistakenly solidfied the wall and applied 
I hope there is an way to make a window on that wall… help please.
One way would be to make the window before solidifying.
Another way is to use loopcut (CTRL+R) and “bridge” using looptools or delete the faces and bridge using the built-in bridge tool.
Other way is to use booleans, it’s generally not recommended, but if it’s a simple wall and a simple hole, I can’t see the problem.
Another way is to use the new awesome knife tool (K) and “bridge” using looptools or delete the faces and bridge using the built-in bridge tool.
PS: LoopTools is a must-have addon imho, it’s disabled by default though, I recommend you to enable it asap, it really makes the life easier.
I use booleans the whole time for cutting windows and doorways. Here is a tip: instead of having dozens of separate modifiers for each window “cutter”, join all the window cutters into one mesh and use that as the boolean cutter. Works a charm.
Boolean? hmm I should try that, though I solved by deleting faces before checking here 