Having done soldering since I was in high school (20 years now) I endorse everything @MazeFrame has said.
You can get rosin core solder and not get flux seperately. Do not get leaded solder. It works better generally but the fumes should be considered toxic. You really only should use it with a respirator and a air evac unit. It will say clearly if it has lead or is lead free.
The most important part of having a good experience with soldering is not the solder (generally), but the iron. Only use a soaking wet sponge or a soaking wet paper towel to clean the tip. DO NOT SCRAPE IT WITH HARD METAL
After you’re done, use a decent amount of flux and solder to “tin the tip”. Then let it cool with a little solder on the tip. Store it that way, it helps protect it.
When you need to heat it up again take the old solder off as soon as you can. Pushing a lot of solder on to the tip will allow the flow of the solder and the flux to really clean it. It will then be ready.
You will burn yourself, it sucks, but it’s not too bad. Hurts for a day or two.
To clean the flux from the solder joints once you’re done (which you should do as it’s slightly corrosive) you can use iso alcohol. 99% -90% is best but 70% will do in a pinch.
All the examples in images are good ones.