You can end your sentence with "...I guess" when you're either not very sure about something:

A: It's not working.

B: You have to have a password, I guess.

You can also use this phrase when you're not happy about something:

I'll stay here and keep working, I guess.

Another phrase that you can use in this situation is "I suppose," which is a little more formal:

A: Is it OK if I send you the payment online?

B: Yeah, I suppose.