Strength training can be simplified. You do not need complicated routines or space age equipment.
The key to building strength and muscle is progressive resistance on basic, effective multi-joint exercises. Add resistance as often as possible while maintaining good form. Adjust your volume and frequency to facilitate strength gains and you will gain muscle.
To build strength and muscle you must focus on the best multi-joint exercises that have the biggest impact, like squats, chin ups and dips, and use single-joint exercises only where multi-joint exercises don't provide adequate loading to a muscle group.
To learn more:
These pages provide some examples of strength training programs for beginners:
The Get Strong! Program can take you from intermediate to advanced stages of strength training and building muscle.
Muscles grow only in response to heavy mechanical loading provided by resistance training. Muscle gains follow strength gains.
To make muscles grow, you have to subject them to progressive resistance. This can come from reduced leverage, iron weights, or resistance bands.
The bottom line is you have to get stronger to get bigger. The following pages provide more details.
Strength training can build or at least maintain muscle while you lose fat.
Fat loss is pointless if you don't have shapely muscle to provide a pleasing physique. You don't want to end up skinny or skinny-fat, if you have any self-respect.
However fat loss itself is a function of diet, not training. When you have fat to lose it means you have consumed more energy-rich macronutrients than you have actually needed. You need to reduce your intake of energy and create a negative fat balance while maintaining a highly nutrient-dense diet. One way is a hypercarnivore diet.
Strength training is necessary to gain quality body weight. Overeating only adds body fat. Adding body fat alone will not make you healthy or more attractive unless you have been anorexic or starved.
Contrary to popular belief, you do not want to eat more than you need to gain weight. You don't gain muscle because you eat more, you eat more because you are gaining muscle! Strength training with adequate and progressive resistance will stimulate muscle protein synthesis, and stimulate your appetite so that you eat enough to increase your muscular body weight.