Another pico-8 practice game (this time with space flowers)

Help
1

I’ve started making another simple game for practice, and the next thing I need to do is make a flower bud (sprite 2) spawn randomly anywhere on the map except the wall tiles marked with Flag 0. I’ve looked at solutions online… but they’re given all at once. I need help to break them into tiny pieces so I understand what I’m doing instead of just copying it. Anyway, here’s my game so far.

Tab 0

function _init()
p={}
px=53
py=63
fx=rnd(120)
fy=rnd(120)
end

function _update()
move_plr()
collide()
end

function _draw()
cls(1)
map()
spr(1,px,py)
spr(2,fx,fy)
end

Tab 1

--move player--

function move_plr()
 
 lx=px --saves player's x location
 
 if btn(⬅️) then
  px-=1
 elseif btn(➡️) then
  px+=1
 end
 
 if collide() then --sends player back to last x
  px=lx
 end 
 
 ly=py --saves player's y location
 
 if btn(⬆️) then
  py-=1
 elseif btn(⬇️) then
  py+=1
 end
 
 if collide() then
  py=ly -- sends player back to last y
 end
 
 if px>=120 then
  px=120
 elseif px<=0 then
  px=0
 end
 
 if py>=120 then
  py=120
 elseif py<=0 then
  py=0
 end       

end

Tab 2:

--collision--

function collide()

 local tl={x=px,y=py} --top left corner
 local br={x=px+7,y=py+7} --bottom right corner

 --get flag 0 for all corners of sprite

 local c1=fget(mget(tl.x/8,tl.y/8),0)
 local c2=fget(mget(tl.x/8,br.y/8),0)
 local c3=fget(mget(br.x/8,tl.y/8),0)
 local c4=fget(mget(br.x/8,br.y/8),0)

 return c1 or c2 or c3 or c4

end