Find a beatbox or drum machine that is within your price range. There is really no difference between a high-end metronome and a low-end metronome. They will beep just the same.
Buy some cheap speakers to hear the metronome in. You don’t actually even have to buy speakers. You can use headphones if you like, but that may drown out the sound of the instrument you will be playing.
Set the beatbox or drum machine and the speakers within earshot of where you will be playing. The metronome should be close enough for you to adjust the tempo and volume while you are playing.
Select the tempo you wish to play your instrument at. Beatboxes and drum machines usually begin with a default tempo of 120 beats per minute. Since you will probably not have an exact BPM setting in your head when you begin practicing, it is a good idea to start from 120 and adjust the speed until you reach a setting you are comfortable with or that sounds natural with the song. Sometimes the beats per minute will be written down at the beginning of the piece you are practicing if you are reading music.
Play your instrument or sing along with the metronome. The metronome should be counting out the beat in 4/4 timing, but that can also be adjusted on the beatbox or drum machine. Adjust the volume level so you can hear the clicks audibly but still hear your instrument predominantly.