you don't say which intercept.
If you want the x-intercept, that's where y=0, so
-x+0 = -6
x = 6
(6,0) is the x-intercept
If you want the t-intercept, that's where x=0, so
0+3y = -6
y = -2
(0,-2) is the y-intercept.
If you have the ordered pair (3,?), plug in x=3 and you have
-3+3y = -6
3y = -3
y = -1
(3,-1) is a point on the line.