Hello and welcome to the board. Have you done all the usual - rethreading top thread, taking bobbin out, changing needle? Is the bobbin in the right way? (I once spent the best part of an afternoon as a new quilter before I figured that one out, lol)
If you've done all that and the needle is the right size for the thread you're using, then it's probably tension. Generally speaking, if the errors are on the top, it's your bottom tension - if the stitches are skipping underneath then it's often the top tension.
Good luck!