69 valiant electrical gremlin turn signal and license plate light

69 valiant. Here is current situation

• license plate light does not work. I have swapped bulbs and nothing. Sand papered connection where bulb goes in; still nothing. I have heard about ground and using a test light but need guidance how to use it to check. It seems simple; clip ground and touch stuff but where to touch.
• Front left turn indicator. When the headlights are off; indicator works as it should. when headlights are engaged, turn light stays lit orange and does not blink but inside the car the dashboard is showing that the blinker is working. Also, I have cleaned connections on ground wire. again, where would i use the test light to check where the ground short is?
• I don't mean to sound stupid, but i have never worked on a car in my life but i am determined to learn. Thank you for any responses.