How do I retrieve something on the hard drive that I put in the trash on a PC?

Putting something in the trash doesn't automatically delete it. Check to see if its still in the trash. If it is, you should be able to restore it. If its not there anymore I can't help but hopefully someone else will come along and be able to

If it is still in the recycle bin you should be able to restore it

Open windows explorer and go down to recycle bin and if you see item on right, right click on it and choose restore

How do I retrieve something on the hard drive that I put in the trash on a pc?

If you mean the Windows recycle bin, right-click the Recycle Bin, choose Open or Explore, and then right-click the desired file and choose Restore. If the Recycle Bin has already been emptied, one approach is to use commercially available undelete software (example: WinUndelete (http://www.winundelete.com/)) to recover the file. The more the computer is used before the file is recovered the less the chance of successful recovery.