How can I build more muscle mass with my dumbbells in my bedroom?

I need some advice on dumbbell exercising. I want to focus on build muscle mass. Are there any things I should know about to help me? I don't have a bench or anything fancy, just 20kg dumbbells and my bedroom...

Thanks.
Sometimes I wish I’d be a man...to be stronger, make more money for the same job, could sleep with people of the opposite sex who would be half my age and having kids without having to bear them.
But sometimes I’m glad I’m a woman just needing to do calisthenics and

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