Whether training for fat loss, muscle gain, fitness or performance, you can't go too far wrong by spending the majority of your time utilising the 'biggest bang for your buck movements.'
These are known as compound lifts, and will always require more than one joint articulation, therefore recruiting more muscle mass, and overall effort.
Examples include, but are not limited to, Squats, Deadlifts, Bench Presses, Shoulder Presses, Cleans, Rowing Movements, Dips, Press Ups, (typically the most exercises that utilise a barbell or a dumbbell) and all of their variations.
We also have what we refer to as 'isolation' exercises, where only one joint is required to move to perform the exercise, and this will isolate a particular muscle. This is fine for things like injury rehab, or for somebody trying to bring up a specific muscle group.
The reason for this is that you will burn far more calories performing Compound lifts vs Isolation lifts, because of the amount of muscle recruited, and the effort required.
You will, therefore, stimulate more muscle mass by using compound lifts vs isolation, which is optimal for building muscle.
For fitness, again, the compound lifts will be a better choice here. Because of the amount of muscle recruited, your heart will be working harder, and you will elevate your heart rate higher than performing isolation exercises.