Want to start working out. Any ideas?

I'm a couh potatoe. Nobody ever says I should do sports (except my doctor because I have constant low blood pressure) because I'm very skinny. I don't look unhealthy, but on my "how do I look" question several people said working out would be great for me. So here I am wondering what I should do exactly?(No yoga please)
Want to start working out. Any ideas?
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