Loud noise and smoke when putting in gear

definitely sounds like the belt. it could be that it’s not the right belt for your mower (not the right length, too wide, etc.), or it is not installed properly. sometimes one of the belt keeper tabs may be out of position, or you could have an issue with one of the pulleys.

search your mower model number to find the correct size and type belt. in the owners manual for that mower (and sometimes on a label somewhere on the mower) you can find the correct routing for that belt. otherwise, see if one of the belt keepers is bent, or out of position, and check the pulleys for problems like being damaged, or loose, or frozen in place, etc.

for more help you’d need to be a bit more specific. provide the make and model number, for instance. also, is it a motion or mowing belt? does the squealing and smoking occur without engaging the actual mowing deck? the more specific you can be the greater the chance someone might be able to help. Good Luck!!