Building a model railway baseboard can be as simple as a piece of plywood from a hardware store
Build a good set of baseboards and the rest of the layout will be easy. It's simple truth no matter how much fun you have constructing scenery or buildings, if the baseboards have cavernous gaps between them or the track bed sags, you'll always wish you'd put more time in earlier.
I'm rubbish at woodwork, but I have found various ways to cheat and still produce an acceptable result. To be honest, I'm so happy with the methods I used twenty five years ago, I've not seen fit to experiment further.
My Melbridge Dock layout was built using 9mm plywood. Each board is 3' long and is nothing more than a top with 6" deep beams around the bottom. There's no cross bracing underneath to get in the way of the point motors and I didn't even varnish the wood. Despite over 100 shows, the layout still works as well as it did when we built it. It's light enough to be lifted in and out of the car by one person too.
Rather than bolt the baseboards together, I have used loose pin hinges attached to the sides. These are available from DIY stores. There's no need to try and remove the pins from normal hinges to make them, the real things have large heads on the pins that are easy to grab with pliers. As well as holding the boards together, they take care of track alignment so there's no need to fiddle around with bolts when setting the layout up, just pop the pins in and go for a cup of tea. This works well in OO, O and even finescale 3mm scale so we're confident it will be fine for everyone.
Being hopeless at woodwork, I prefer to get the plywood cut for me. My local hardware store offers the service but so do many wood yards and even B&Q. After this, I just glued and pinned the bits together. Here's how.
What we used
30mm panel pins
Loose pin hinges