Tampons can be tricky if you're new to using them. One of the things that can actually have a big influence on the ease of getting them in or out is the position you do it in. When you try to insert them, are you sitting? Standing? Laying down?
That fear that if you have trouble inserting a tampon you'll have trouble having vaginal sex is a common one. But, in most cases that isn't what ends up happening (in part because there's lots of ways to have sex that don't involve putting something in the vaginal canal). One of the reasons for this is that, when you're aroused, the vaginal canal loosens, your body produces more lubrication, and the cervix pulls up to create more room. That's a very different situation from when you're putting a tampon in; you're probably not aroused, and you may even be extra-tense because you're worried it will hurt. Does that make sense?