Lots of little differences, like therapists are usually better at being objective & helping you see what actions are rational vs. irrational, they’re trained in active listening and don’t talk over you or redirect focus to them, comfortable with outburts of emotion and don’t shy away from tears, can give you homework based on years of training, etc.
Biggest difference though? The knowledge that this person is a professional and that your emotional problems are not a burden to them. The ability to fully express your emotions, without qualifiers like “but it’s fine, I’ll figure it out” or “there’s nothing to worry about, I’m handling it” etc. The feeling of relief when someone else shares the weight of your grief without it draining them or causing them pain.
Therapy isn’t just beneficial to you. It’s beneficial to everyone who loves you.