[Radioroslyn]

Well there are two ways. One is to whip out your handy dandy 1940 tube manual and look it up. Nowdays I look  it it up online. Some schematics have the pin numbers indicated on them some not.

I think you maybe be asking how do I count pins on the bottom of a tube?

Older standard base tubes: 4, 6, and 7 pin tube are simple. Find the two fat pins looking  from the bottom. Face them towards you. The pin on the left is pin#1 count clockwise to determine the others. For instants a 4 pin tube pin 1 is the fat pin to the left. Pin 2 is the thin one above it. Pin 3 is the thin pin to the right of pin 2. And pin 4 is the other fat one.
On the 5 pin tube two of the pins are closer together. Pin 1 is the one on the left of two that are closer together, pin 5 is the one to the right of pin1.
Schematics that don't pin numbers doesn't mean that the connections are layed out in the order in which they appear on the schematic.

I see I'm late to the party! Slow typer.