If you have no prior experience in weightlifting, starting a beginner program like Stronglifts 5x5 is a good way to gain muscle quickly. Weightlifting technique is important to prevent injury, so watch some youtube videos on the basic lifts (squat, bench press, deadlift, military press, and Pendlay row) so you can keep your vertebrae in place.

In terms of food, start weighing what you eat and try to track your carbs and fat. To gain muscle you'll want to get at least 120 g protein a day and to avoid gaining too much weight you want to keep protein as a fairly high proportion of calories, 25% at minimum and ideally around 30. Carbs should be 40-50% with the remainder as fat - carbs will be what enable you to recover quickly after your lifts. You may need to increase calories - 120 g protein @ 4 kcal/g @ 25% of your diet is 1920/day, while you might want upwards of 2500 (150 g protein) on your lift days and 2000 on your off days. If you enjoy it, throw in some light to moderate cardio in your off days and then wait for the gains to roll in.

The hardest part of building lean muscle is making sure you're getting protein from comparatively low calorie sources, otherwise you go over your calorie requirements and start adding fat as well.