Most of the spirits you hear people talking about want to be summoned and to provide you with their powers and abilities. By summoning the spirit, you give it the opportunity to make itself stronger by manifesting its power in the world and in your life. If a spirit directly harms you, then either it is a parasite that should be banished, or you have confused the spirit doing what you asked and maybe even protecting you with something that appears bad. Summon a spirit for money, and then you lose your job, but then find one that pays way better. Seemed bad at first, but it was just the process to getting exactly what you asked for.
You can banish after the ritual if you want to, and there have been times when demons have “threatened” me and tested me to see if I was strong enough to give them the boot and so be worthy of telling them what to do. Normally, though, it doesn’t make sense to banish because you presumably want the spirit to be around. You summoned it for a reason, right? Do you call up the plumber and then kick them out when they show up to do their work? I think it is best to welcome the presence of the spirit, as that shows that your magick is working and that the spirit heard your request and is with you.
Protection depends on what style of magick you are doing. Good magickal methods will have some way of connecting you to the fundamental underlying consciousness that energizes and empowers all magick. Sometimes this is a mantra, sometimes it’s Godnames, sometimes it’s some kind of visualization. Usually you don’t really need any protection because the spirit is not out to get you. If you encounter any malicious entities, then there are protection spells and banishings that you can perform.
You’ll hear all sorts of opinions on banishing, so I’ll say, imo, that unless a grimoire specifically says not to banish, then it’s not going to hurt. If you don’t want to do a more involved ritual, a simple, quick banishing is a good way to stay connected to magick. I’d advise you not to get stuck in the mindset, though, that if you don’t banish all the time then * something bad * will happen. I banish with certain rituals that are more lengthy and involved, more as a way of centering myself, not because I’m spooked, but most of the time I don’t. Do whatever you’d like.
My first ever ritual I fondly call the “astral spunk” technique. It’s just the chaos magick sigil masturbation magick you can find all over the internet. I wrote out my intent (with some bombastic phrase like “IT IS MY WILL THAT THE UNIVERSE SHALL BEND TO MY COMMAND BWAHAHHA”), mashed the letters together into a sigil, had a wank, and then felt weird and kinda forgot about it. That ritual’s still working to this day. My sex magick now is a bit more sophisticated but sexual energy is just so damn potent.
I’d suggest that you purchase a grimoire, a book of magick, that appeals to you, give it a read, make sure you understand the instructions and what to do, and then do the magick. Then do it again. If you keep doing magick, you’ll make your life magickal.