Hi!
I was looking through the tutorial>pattern effects and noticed the letters in those effects (‘F’ for example)
I just dont understand what those mean, could anyone explain?
Thanks. 
Pattern effects are based on hexadecimal numbers containing digits 0 to F (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F). Enter them as you see them in the tutorials.
in general: those are hexadecimal numbers. hexadecimal means 10 isn’t ten, but sixteen.
1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f (where a = 10, b = 11 … f = 15)
wiki article on hexadecimal numbers
it’s a number system based on 16. our normal numbers are based on 10. meaning:
101 = 1 * 10^2 + 0 * 10^1 + 1 * 10^0 = 100 + 0 + 1 = 101
perhaps you know binary, there 101 would mean 5 in decimal, because:
101 = 1 * 2^2 + 0 * 2^1 + 1 * 2^0 = 4 + 0 + 1 = 5
101 in hexadecimal would be calculated as follows:
101 = 1 * 16^2 + 0 * 16^1 + 1 * 16^0 = 256 + 0 + 1 = 257
(x^0 is always 1. independent of what x is.)
besides that those hexadecimal numbers are there for two things: identifying effects and specifying values for effects. generally the effects “belong” in the effect column. but there they affect all notes in the current track, so you can use “shortversions” of most effects in the pan/vol columns to just affect one certain note column.
for example:
c-401 E3.. ....
here you have the retrigger effect Ex in the volume column. so it just affects this particular notecolumn. the E identifies the effect and the “3” is the value for the effect. (meaning renoise is supposed to retrigger the note every 3 tics)
bottom line: the “letters” are just numbers. the “left” numbers normally identify the used effect whereas the “right” numbers normally are the values the effect uses. it’s not that complicated and the tutorial pages are actually quite sufficient once you got the “basics”. so have fun o/
look at the bottom left of the screen when you enter a number/letter - the tips will tell you what each one does