Is x+3=-1 horizontal vertical or oblique

and is 1+y=0 oblique vertical or horizontal and last but not least is x+2y=8 horizontal vertical or oblique

ye great you tell that, but if you dont explain it nothing will be learned

x+3 = -1
if you substract 3 from both sides you get
x=-4 this means that x is fixed. and since y is vertical and x horizontal, a vertical line will be the result at x=4

1+y = 0
really by doing something similar, substract 1
y = -1 this means y is fixed and since y is vertical and x horizontal, this will be a horizontal line at y = -1

x+2y = 8
this one is a bit less logical maybe for you? and harder to understand for sure!
i'd move it so that its easier to understand, by substracting x and dividing by 2 id turn this into:
y=0.5x + 4
now this means whenever x gets 1 value bigger, Y gets 0.5 times that value bigger, and if y gets 1 bigger x wil have to get bigger by a factor 2 to compensate, since 4 cant change
also: if x = 0 y = 4 so it will cross y in (0,4)
going by these factos we can determine this one to be oblique

Anything that has only one variable is a straight line. Since it's x=-4, that means the line goes through x=-4. It's a vertical line. The second one is horizontal because it goes through only y=-1

Since x+2y=8 has two variables, it is oblique.

x+3=-1 is vertical. Here's why.

x+3=-1
-3 -3
x=-4

1+y=0 is horizontal. Here's why
-1 -1
y=-1

x+2y=8 is oblique. Here's why.
-x -x
2y=8-x
/2 /2 /2
y=4-x/2

the first one is Vert
the second is Horiz
the third is Oblique