I’m going to answer for the little planes, since that’s what I know.
These days, there is frequently a “push-to-talk” switch mounted on the pilot’s (and usually the co-pilot’s) main control device - either a large, joystick like object or something vaguely reminiscent of a steering wheel called a “yoke”. If it’s a stick, it’s usually on top of stick, if it’s on a yoke it’s usually on the left for the pilot and right for the co-pilot. Usually it’s a small red button, positioned so a thumb can easily shift to reach it. If you’re going for that option, put on the pilot’s headset (if you aren’t wearing one already), then gently push the switch. You’ll hear a sort of click. Start talking. “HELP!” is a good start. Release the switch. If you get a reply, you did it right. Remember that they can’t answer you unless you take your finger off the switch.
If you can’t find the PTT switch - and if it’s a real emergency, don’t spend too much time on that - there is usually a hand mike mounted on the instrument panel between the pilot seats. It’s a plastic lump with a coiled cord attached to it. Pick it up. There is a switch of some sort on the side. Put the business end real close up to your mouth, push the switch, and talk. Relase the switch. If you did it right. you’ll get an answer.
The radio is usually mounted to the right of the pilot in the left seat. There is some resemblance to a CB display. There may be more than one, so it can get confusing. If you can figure out what gizmo on the panel is the radio and how to tune it, turn to frequency 121.5 - it’s the aviation equivalent of 911. Yell “HELP!” You will get a human on the line very quickly, it’s monitored by a lot of agencies. But if you can’t don’t worry about it - yelling “HELP!” on just about any frequency will usually get you assistance.
The Worst Case Scenario series of books has a decent chapter on how to land a small plane. Read it. Microsoft flight simulator has some decent panel displays for several varieties of airplanes (including the big jets). Proper utilization of this software will not only provide hours of entertainment, it will also enable you to identify many varieties of airplane equipment.
Of course, none of this is a substitute for real flight training, but it could give you enough knowledge to save your butt in an emergency.