[unsung]

A couple people had some great comments that should get you started; I'd just like to add that you don't need to do everything at once either and your workflow can be flexible. When I'm making a board with weird parts, I like to first just go into the symbol editor, make a new project library, and draw out whatever I need for my project with the correct pin assignments. Then at least you can focus on copying the schematic over and getting the ball rolling.

Once you are happy with the schematic, and parts are roughly placed where you want them on the board, you can go ahead and jump into the footprint editor, make a project library in there with the same name, and draw the physical copper layout for your tubes or whatever else to attach to based on datasheets or caliper measurements. Then you run footprint assignment to match up all the symbols with their corresponding footprint, and update the PCB to populate it with parts to lay out. Once the parts are placed logically where routing will be sane, follow the ratsnest connection lines to get your board routed.

Last you want to go to your manufacturer's website, look up all their specifications on board construction [0], and make sure all their recommended design rules and board stackup are plugged into board setup. This may mean going back and changing some trace sizes, trace placements, vias, and so on to pass design checks. Later you will do this earlier, but it's better not to get bogged down at first and just start designing, and you'll learn why things are routed as they are.

After this, spend time inspecting your board, looking for errors, making sure all checks pass and everything makes sense after a few reviews. Then export your gerbers and drill maps and send the zip to your manufacturer.

It's a little daunting at first because there are just a lot of steps between a schematic -- essentially a cartoon version of what your circuit will be, and a layout -- what your circuit will actually look like. You don't have to do every step at once and once you have the schematic drawn, you can just keep adding to it until you have something that works.

[0] https://docs.oshpark.com/design-tools/kicad/kicad-design-rul...