Tina, to make what I'm gong to write easy to understand, please realize the the London Undgerground and the Tube are the same thing. Officially, it's called the London Underground but most people just call it the tube.
The Trains that take you into Paddington and out of Victoria are not the same type of trains that will take you between Paddington and Victoria. That's done on the tube.
At Paddington, you won't just walk over from one platform to another to get the Bakerloo line. You have to walk over the the London Underground station at Paddington, and go down to the tube lines. At Victoria, you'll go from that tube station to the Victoria train station.
With the underground, rather than looking for platform numbers, look for the names of the lines and determine which direction you need to go.
Have a good trip.