網球拍穿線問題

For a beginner, string does not matter that much.
Any cheap one would do.
There should be a label or print on the throat of the racquet indicate the tension range. If no label 50-60 lbs. are safe for most sticks.

It depends on your choice.
I play more than 20 years and I want to change the strings often, so I use Synthetic gut about $120 for 1 week.
You can use Real Gut $700 which is good feeling.