Just joined forums because IDE is proving me a hard learn

I've been working with the IDE for a few months on and off, most of the code taken from various sources; I recently encountered a moment- which still persists- in which the various programs I had completed and had been proved as working stopped working. My issue is I can't decipher error messages to save my day.

Most of the messages look along the lines of this:
C:\Program Files (x86)\Arduino/DHT_and_LCD_datalogger_tester.ino.ino:51: undefined reference to
.....
... unsigned char)'

I moved something around one day and then deleted the folder (had been newly introduced after programs were proved as working) caused everything to become problematic for me.

I'd appreciate your feedback. Thank you!

Looks to me like your problem is with the ... ... .. on line ....

Pete

I'd appreciate your feedback.

No, you wouldn't, if you don't post the code and the EXACT error messages.

Sounds like you deleted/moved the libraries folder.