@lwolfe it is a common misconception, but muscle doesn’t “replace” fat; however exercise can shrink fat cells and grow muscle cells! but it seems like weight training would help you reach your goal of being more “toned” aka building muscle definition! so you don’t necessarily need to focus on weight loss if you just wish to have more muscle definition.
it is important to eat enough calories when weight training to make sure you are fueling your body properly. that is number one. i’d recommend starting with low weight and only one or two sets per exercise, as you may be sore the next day (which is not a bad thing, but if you overdo it you may need to take a bunch of days in between workouts which is not ideal for building muscle). you can even start with just body weight exercises if adding additional weight is too much right now.
i would aim for one or two exercises per muscle group for now (for example squats and lunges for your quadriceps, deadlifts and hamstring curls for your hamstrings, etc), around 8-12 repetitions per exercise, and you can do one or two sets of each. watching videos on proper form is helpful as you don’t want to hurt yourself! especially when heavier weight is involved.
i find that beginners usually find 3 days per week, focusing on full body, easiest to start out with.