Start working out.
Calculate your daily intake of calories. You'll need around 2500-3000 calories everyday to not be calorie deficit, which you should take care of.
As a thumb rule, 0.8gm of protein per pound of your body weight everyday.
Eat a lot of carbs. Carbs will help you get bulked up.
As already suggested, be regular. Make gym a part of your routine. Don't do it for temporary gains.
Yes, work out and eat healthy. Stay fit to enjoy your life before it is too late.