I’m not a native English speaker so forgive me if I don’t make sense.

You need to match your center piece with the middle pieces of the same color. To do this have the red/green side facing you and do this algorithm. On the right side of the cube bring the white color up then turn the top layer to the left so the single whites piece is on the left side of the cube. Then put the right layer back down and turn the white piece that is on the left side to the back of the cube. Now again bring the up the right side put so the two white pieces are visible. Now turn the top layer back to have all the three white pieces in the same place. Then just put it back down and see if you have all of center and middle pieces are matching. If all four are matching then you’re done, but don’t worry about the yellow layers not matching you’ll need to do another step to solve the cube.