gonna anon this as there is some quite *personal* advice from experience here.
I must have tried about 10 times to put a tampon in before finally succeeding- don't give up! you might be scared that you just can't do it/ there is a problem- but don't worry, everyone I know has gone through that and realised that it was just normal to find it hard to begin with.
One of the most important things is to remember to relax. I really can't stress this enough. Get in a comfortable position (I would suggest lying down), using a mirror is also deffinitely helpful, and take your time. try "bearing down", sort of like pushing or a pelvic floor exercise, you will feel your vagina contract, this opens it up a bit and may make it easier. DEFFINITELY use applicator tampons, I have been using tampons for about a year and still don't use any other kind. make sure you get PLASTIC, not cardboard, they are much, much easier to use because they are smooth. Buy some "lights" or "teen" ones, they will be smaller and specifically for beginners.
And lastly, lubrication. If you are dry it will be very uncomfortable. Either use vaselline or (this does work better, but it's up to you) - masturbate beforehand. it really does make it easier, you wouldn't have sex without being turned on, afterall, and natural lubrication is the best kind. It also opens up and relaxes your vagina, making it easier to insert a tampon.
keep trying! good luck.