How do I find B in y=mx+b?

If you already have an equation, all you have to do is locate the slope and look after it. But if it's in a graph, it's where the line is crossing the y-axis.

An example of the equation would be

y=2x+3

y=mx+b

2 would be m which is slope

and 3 would be b which is the y-intercept