>>2038321No worries. There was a time when I didn't anything about bikes, except that I liked riding them. It looks like model of bike vertical dropouts, and comes with a cassette rear wheel.
With singlespeed, you still need some way of tensioning your chain. Right now, your rear derailer is doing that work. There's five ways I know of doing it.
Easy mode is having a frame with horizontal dropouts/track fork ends, so you can scoot the wheel back and forth a little.
You can also mount a 'chain tensioner' or old rear derailer, and use the springs inside that to tension your chain. This is what I'd recommend.
The last three all work, but they are either expensive, or tinkerer's projects: eccentric rear hub/eccentric bottom bracket, 'ghost ring', 'magic gear'.
What I would recommend is using an old rear derailer. No shifter, no cables. The idea is you wind both the high & low adjustment screws in, to match the position of where your cog is. (The screws also prevent the RD from moving in or out.) From there on, the springs inside the derailer tension your chain.
If you look at a Paul Comp Melvin, you can see how it's kind of a stripped down derailer. There are other designs, but they all boil down to the same idea: at least one spring and one pulley to tension your chain.
Because you would be single speed, any derailer would work, but road ones with short cages are slightly better, just because there's less of an arm sticking out/less to bend. When putting it together, you cut your chain to an appropriate length, so that the RD is somewhere between half-tensioned and maxed out. But there's a fair bit of leeway--you can always take another link out of your chain later.
