There are terms for what I'm describing but instead I'm going to explain as best as I can.

You could learn a small portion, or all of, "Hey there Delilah" by Plain White T's. It's a good introduction to playing a drone note followed by two other simultaneous notes. You can take that riff and instead of playing the two notes after the drone note together, play them in ascending or descending order. Isolating three fingers to play their own string, in time, is the key to finger picking. It's no different than adding notes or extra strums to a measure. You have to make it fit on the measure.

But if you'd like to give each finger it's own "brain" fast, you then run any major scale. Run the scale with just your thumb, then each individual finger, then add a finger and alternate with each note, and finally add the ring finger once you have alternate strumming with two fingers down. This helps give you confidence in knowing where the string is with your finger tip as well as developing natural anchor points for your hand on each string.

Once you can kinda do those things seperate, with some mistakes, start to add each individual technique. Drone the low E with your thumb and alternate pick between your index and middle finger.

Ex. 3rd fret low E string with your thumb, 3rd fret A string with your pointer, 5th fret low E string with your thumb, 5th fret A string with your middle finger.

Once you're confident with those three fingers strumming, add the drone of the A string and move your two fingers down one string respectively.

Ex. (You can add this to the end of the previous example.) Open A string with your thumb, 2nd fret D string with your index, 4th fret D string with your middle, open E string with your thumb, 5th fret A string with your index.

Once you get comfortable with the pattern of thumb, index, middle; switch to thumb, middle, index and eventually a mix of those two. You can try to incorporate the ring finger but you won't run into that unless you want to play Fleetwood Mac level songs.