BJT is also known as Bipolar Junction Transistor. MOSFET means Metal Oxide Semi-Conductor Field Transistor. The parts that they have are different from each other. The BJT is known to have the base, the collector, and the emitter. The MOSFET will come with the drain, the source, and the gate. If you would need the right tool for low current applications, the BJT is going to be ideal to use.
If you would need to use something for high power functions, the MOSFET will be the better option out of the two. These can help change the power signals effectively whenever you would need them as long as you would use them correctly.