Building muscles. Of building muscles?

Hello doctor, since I was in class 7, I have a very big biceps. All my friends Will see me with envy. I focus solely on building biceps. My biceps looks like a hard leather cricket ball. My hands are very strong. But except my hands, all other parts of my body doesn't seem like muscular. What should I do to strengthen my muscles all over my body. For building muscles, What should I do? I'm on my weight loss program currently. Should I start my strength training exercises along with the weight loss of program or should I start my strength training exercises after shedding my extra pounds? Is it very hard to build muscles? I don't want to be a big frame bodybuilder. I just wanna improve my strength and look muscular, that's it. Will it take a long time? What is the mechanism of building muscles? Help me. Thank you.