Archaeologist Professor Clive Arno stumbled upon some ancient coins which were able to transform whoever held them into superheroes; the professor thus became Capt. Action and his son became Action Boy. Their arch-enemy was Dr. Evil, also adapted from the Ideal action figure line.
The series itself, although it lasted for only five issues, was actually pretty decent. Veteran Gil Kane was the main artist on the series, but it also boasted the talents of Wally Wood (artist) and Jim Shooter (writer). Kane himself would also write a couple of issues in addition to his artwork. Superman guest-starred in the first issue; although not quite a part of the larger DC universe, the title's presence was a brief bit of variety for comic readers of the time.
Turning a popular action figure into a tie-in comic sounded like a sure path to success; and, a decade later, it was - just not for DC, who did this series. Marvel would enjoy healthy sales with its Rom [The Spaceknight] title from 1979 to 1985 - it would last 75 issues and 4 annuals, enjoying popularity long after the toy itself stopped being manufactured.
You can read about the Captain Action toy here.
You can view all 5 of the Captain Action comic covers here.