This subreddit is pretty helpful and has a helpful faq.
faq - xxfitness
Find out your Total Daily Energy Expenditure (TDEE). This is basically how many calories your body is estimated to burn throughout a normal day. Here is a simple online calculator to find that number for you.
Accurate Calorie Calculator - Scooby's Home Workouts
Download a calorie-counting app or sign up to a website where you can track what you eat. You can also do this manually in a book or a spreadsheet. A good tracker should be able to show you calories consumed, as well as the protein/fat/carb values of the food you eat. MyFitnessPal, Loseit, and Fitday are all great websites for doing this.
It is recommended that if you use any of these websites, you set your own goals rather than relying on the ones they offer you. To work out how many calories you should have, take your TDEE and:
Add 10-20% to gain weight (for example if you're trying to build muscle or are currently underweight)
Subtract 10-20% to lose weight (for example if you are currently overweight or trying to lose fat)
Eat your TDEE to maintain weight (for example if you're just trying to improve heart health without changing your body composition)
Female, 5'3", 50, Starting weight: 163lbs. Current weight: 135 (more or less).
I can squat 187.5lbs, press 75lbs and deadlift 200lbs