It is widely reported that former FBI attorney Kevin Clinesmith will plead guilty to altering an email. He thereby falsified the Carter Page FISA warrant and helped the FBI spy on the Trump campaign.
What you should understand is that guilty pleas like this are normally made to reduced charges. For instance, "If you'll plead guilty to this lesser charge which will carry a light sentence, and testify against your coworkers, we won't try you on a more serious one which, if convicted, could put you away for a decade or two." It's amazing how persuasive that offer can be.