It is "strum a guitar" for playing a guitar. "string something (tie attach to another or a fixing point) " "string the boat to the mooring" although "tie" would be more common to a lay person You can basically string anything that requires string or some sort of cord instruments fishing nets etc. string would be used to describe making maintaining preparing anything that require string. and "tie" would be the common word for joining attaching anything or anyone to anything or anywhere.

String some lights across the room. String along: tag alongside, join. String up the tomato plants: to tie them to a wire frame so the heavy tomatoes don’t bend the plant.

To string words together. To string someone along. To string bits and pieces together.

You string a racquet. You can string beads to make bracelet or necklace. Besides a guitar you can string any string instruments.