I want to go to the gym, but I feel insecure about my body. What should I do?

I want to work out, so that: 1. I will be more healthy; 2. I will look more attractive for girls.
But I am insecure about my body. I am too skinny, and I am afraid I will be laughed by those who go to gym regularly.
What can I do?
I want to go to the gym, but I feel insecure about my body. What should I do?
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