I'm an amateur astronomer. How do I read the right ascension on my planisphere?

Answer 1

You read Right Ascension and Declination just like you do Longitude and Latitude on a globe. The difference is that Right Ascension (RA) is measured in hours, minutes and seconds, and starts at the Vernal Equinox and only increases in one direction whereas longitude is measured in degrees, starts at the Prime Meridian and increases to the east and to the west from 0 to 180.
In general, each hour of RA is equivalent to 15 degrees. So if you start at the Vernal Equinox any star on that line (as I recall Caph is pretty close to it) will have a RA of x hours, y minutes and z seconds.
Each star has a specific RA and Declination, but RA is often confused with Hour Angle (which starts at an observer's eastern horizon at 0 to the western horizon at 12 etc.) RA+HA=ST (sidereal time)
The links below can illustrate better than I can describe.