Caloric Excess. I am unable to post links yet but find a calculator that guesstimates your calorie maintance (maintance= calories burned and calories consumed being equal, deficit= calories consumed is less than calories consumed, excess= calories consumed is greater than calories burned). By finding out your maintance you are able to find a starting point to how many calories a day you need to consume. Secondly comes your goal of weight gain, dirty or lean. If you want lean mass gained (as little fat as possible) you eat enough lean foods (chicken, turkey, red meats, etc..), vegetables, etc...to hit that caloric excess. This is harder because you must eat a lot more in order to hit that goal but produces more satisfactory results. Or you can dirty bulk in a sense where you just eat everything you can to reach that caloric excess you want. Don't take this as eating fast food all the time, cause yes your muscles may grow but so will your gut. Just think of it as less observational of what you eat and shovel food in your mouth.
For me, I cook my days food the night before. Lots of chicken and meat for my lunches and make a couple peanut butter sandwiches. In the morning I have 5 eggs with multiple sides (mostly vegetables) and at night whatever we have in the fridge. If I'm unable to cool that much or skipped out on something cause work got busy ill stop at chicfila get 2 spicy chicken sandwiches (1000 calories right there). My body is able to cut well so I don't really care to much about adding in some fat as long as I hit that caloric excess to a good degree (at 6'3 212lbs active lifestyle I burn about 3500 calories a day so I must consume 4000-4500 calories a day.
As you see it all depends on the person, their lifestyle, and your goals. Again I wish I could post links but since I can't just google "strong lifts caloric excess" and it should be first link on page and do that reading its good. There are also plenty of information and logs you can get an idea from on this forum.
Thank you for your read