Dwell is how long the points are closed (in degrees of crankshaft rotation) before each coil firing. The spec ensures there is sufficient time for the coil to saturate (similar to charging a battery) for a strong spark. A dwell meter is used to set the points to the specified degrees. They are often available for a couple bucks at garage sales and swap meets, or online auction sites. I just did a 30-second search and found a FleaBay auction for a timing light, compression tester, and a dwell meter, all for 99 cents and $12 shipping.
Dwell can also be set with a simple continuity light, and a degreed damper, simply turning the crankshaft by hand and noting the degrees that the light comes on and when it goes off. The difference in degrees is your dwell. You can also then set your initial timing (base timing) with teh test light once the dwell is set, as your initial timing will change when the dwell changes.
Different brand distributors have different point-cam shapes, but there is often a "get-by" spec to set the points by gap when a dwell meter is not available. While it should still be set with the meter to get the best sparks, most stock Fords will get up and running OK with a .015" to .017" point gap. In a road-side situation, a "standard" business card is about .012-.014" thick, and a matchbook cover is about .015" thick.
David
PS: Points are very difficult to get right by setting a gap and then tightening the screw down. In-fact, most have a slot or tab, that once the points are roughly set and the screw snugged-down pretty tight, they can be gently but firmly pried from side-to-side with your screwdriver to set the final gap.