Make hobbyist PCBs with professional CAD tools by modifying "Design Rules"

Step 5 Autorouted using the defaults, and what's wrong with it...

Then we fiddle with the autorouter a bit, being careful to set the top later direction to "N.A." to get a one-sided board (but using all the other default settings.) We gets something that looks like this.

That actually looks pretty nice. So what's the problem? The problem is that if you try to make that board in your kitchen, you'll probably be in for a lot of frustration. There are two main issues:

1) Trace width. The default trace width is 10mil (a mil is 1/1000 of an inch) or about 0.2mm That's fine for most professional PCB fabricators; most can routinely and reliably make boards down to 6mils. But it's VERY fine to accomplish using something like toner transfer (recall that a fine-lead mechanical pencil is 0.5mm - nearly 3 times bigger!)

There's a similar problem with the amount of pad left around the holes; while it's fine for a fancy CNC-drilling machine, if you try to drill the holes with typical home equipment you'll probably end up removing the whole pad.

2) Clearance. This is the space left between tracks (or between tracks and pads.) Like the trace width, it defaults to a small number: 8 mils. that's just not a realistic value for a hobbyist...