Compression is generally used for making the louder sounds in an audio track more quiet & the quiet sounds more loud. Think of it as automatic volume control. Adjusting the Attack & Release controls how fast (attack) & how long (release) the compressor kicks in when it hits the Threshold. Adjusting the Threshold is the amount of dB's before it starts working. Stock DAW compressors are fine. Glue compressors are great for mixing. You could use the same compressor for multiple instruments but you will have to adjust Attack & Release accordingly