Adding to the convo; learn about low pass and high pass filters too. Here's and article: https://www.izotope.com/en/learn/6-ways-to-use-a-low-pass-filter-when-mixing.html
The work exactly as described, you create frequency 'notches' to wade out those competing frequencies. A low pass filter strips out all the high frequencies and leaves all the low frequencies so that you're only dealing with one end of the spectrum. From there you can notch out competing frequencies. This does mean that you have to make choices on which frequencies you leave or notch out between instrument. You have to prioritize and experient to see what works for your ears.