how can u tell which way friction is acting? I know it acts in the opposing direction

[lilac walrus]

how can I tell whether its left or right

oh

is it like the ladder is falling down so the bottom of the ladder is going right so friction goes elft

if that is right ^

then I understand why friction goes up if the vertical wall was rough

also

when we say perpendicular distance
is it perpendicular to that orange line?

[sand mesa]

Yes