Hey there @ImKim! So you did everything right but changing the data type.
So the green pins are floats, what you did with the plus node (red box) was add the player’s Z height, with the forward vector’s X + 50 and y + 50. This results in a single float being passed into a vector. So essentially you just added these floats together to one single number, and changed it to a vector. Basically (example number) 50+51+51 = 152 → Vector (x 152,y 152,z 152) isn’t going to output a proper Vector.
Now take a look at your correct solution, it’s pins are yellow, which means it’s inputting and outputting a Vector. So instead of trying to add the floats together, you’re assigning the variables to the correct X, Y, and Z in the vector, but that’s handled natively by the data structure. Adding Actor location to a multiplied Actor forward vector effectively does this X+X,Y+Y,Z+Z.
Does that clear it up?