Gym Flirting signs? eg Looking etc?

Hey everyone, long story short
I feel like that this guy at my gym has interest in me...
People say when a guy has interest in you he looks at you often, comes near you, has "long" looks/stares at you, mentions you to his friends etc.
I realized that this gym guy happens to do those things "eg looking/staring, near me, him + his friends looks at me" and recently I finally talked to him but it was very short and I couldn't get his name sadly but during the convo he kept smiling and gave me good eye contact. Plus he did treadmill running for the first time (from what I seen through the year) and he aligned with me? strange and I did smile at him one time and he smiled back. :)

Anyway I was wondering if he has interest? (1)
and what would you do if you had interest in a girl/someone at gym? (2)
Gym Flirting signs? eg Looking etc?
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