Butt plugs come in different sizes. If you want to experiment it’s best to start with a small straight dildo or a butt plug that’s not too wide. A small butt plug is about the size of a finger. Jelly butt plugs are better to begin with than butt plugs of firm-texture.
Relax the muscles around your anus. Explore your anus with a finger, using lots of lubrication. Discover the shape of your rectum and let your rectum get used to having something in it. Once a finger feels pleasurable, try a dildo or small butt plug. As it is inserted it should curve a bit toward the belly.
When the butt plug is small it can easily slip out. So if you are used to a small one and you want it to stay in, you have to use a bigger one.
Stop as soon as you feel any pain. Most people feel pain when they are tense. If that’s the case with you, you first have to learn to relax the muscles. You also might feel more relaxed if you take a warm bath beforehand.
To prevent STD’s you should never share sex toys, unless you cover them with a condom.