It’s true. Nutrition is the most important aspect of weight training. The two numbers you want to pay attention to are calories and protein. If you want to gain weight you need to be in a caloric surplus and if you want to lose weight you need to be in a negative. To calculate how much you need there are online calculators or apps. Second number you care about is protein. There is a wide range of numbers for this and people below may suggest different guidelines but I always go off 1.7g of protein per kg of body weight. As to what to eat I’d look at what bodybuilders eat as they need to stay lean and have a lot of muscle. Breakfasts are things like eggs and oatmeal, lunch and dinners are things like lean meat (chicken, turkey, red meat, fish) with a couple of vegetables such as rice and broccoli. I wouldn’t worry about how many times a day to eat just as long as you hit your numbers.
A split workout is where you train different body parts on different days whilst a full body workout is where you train your entire body during the same workout. Some people prefer one to the other but most people would recommend beginners to do a full body workout as you need to focus on basic competence and endurance. I like this workout for beginners but others may put suggestions down below and pick whichever one catches your fancy https://gymtalk.com/arnold-schwarzeneggers-golden-six-routine/. Bear in mind to make the changes to the workout that the article recommends.
Getting Cut is All About Your Diet
Some say the difference in weight lifting is between high weight and low reps and lower weight but with higher reps. The difference between various rep ranges is really not so severe. They don’t really produce different amounts of strength or hypertrophy. Getting cut is entirely diet. What matters most, is number of sets at a given intensity. That is to say there isnt much difference between 3×5 sets that are an 8/10 in difficulty to complete and 3×10 sets that are an 8/10. 5×5 at 8/10 would be better than either though (assuming you don’t outpace your ability to recover).
Now you have to stay in reason, a bunch of 1RM singles probably isnt the same as a bunch of sets of 20 that are to failure, but anything in the roughly 3-12 range will have little difference. Another caveat is that if you train exclusively in one range you will probably get better at that range specifically, but in terms of hypertrophy and general strength its all about intensity (difficulty of a given set) and volume (number of sets). A good program will used a variety of rep ranges. Honestly instead of worrying about this and trying to implement these decisions on your own you should probably get on a program that has been proven effective, you will likely see better results. There are several proven programs in the wiki.