Is a pull up something that has always seemed out of reach? Don't give up, you just may be going about it the wrong way.
Try starting high by standing on a box and stepping off to the side with a slow negative all the way down, then use a step or jump back up to the high starting position. Next time, try the assisted machine, and finally, a band looped under your foot. And remember- if you want it, you have to work for it! Practice practice practice! Once you build the strength to do them with a loop band or a few without assistance, try doing 5 sets 3-4 times a week, each set do one to two less reps than the last set- don't max out every time. You're not (most likely) going to go from zero to three sets of 10 in a week, just stick with it and stay focused 😉