They can be joined together with splicing tape or splicing cement. Wet splicers use a cement that dissolves the surface of the film. Some varieties of Super-8 splicing tape are 8mm wide and cover the full width of the film, with sprocket hole openings just like film. Others or not as wide and won't cover the magnetic stripes of sound film. The first style of tape can be used to repair broken or stretched sprocket holes, although your success rate may vary depending on the severity of the damage.
Wet splices destroy two frames of film.
Dry splices destroy no footage, but poor grades of splicing tape can ooze glue as they age. Making splices that are invisible upon projection is a skill mastered with time, care and patience. Other accessories can be purchased cheaply or made easily. A pair of thin, lint-free gloves will help you keep damaging skin oil off your film. I have a hard time handling film while wearing gloves, so I just wash my hands very frequently.