Help with project please!!

[maxkd]

Ok i am totally new to the electronics game but fascinated also.Can any wiz kids help me build the following in the most simple idiot proof way(so i can understand,yes im an idiot)

Project:want to build battery operated voltage generator with following specs!

0-30 volts(variable)
polarity changes automatically approx 4 times a second
0-50 milli amps(variable) flowing thru to attached electrodes.

I have seen similar projects elswhere but they were more complicated and too advanced for me at this stage.

Would really appreciate any instructions,diagrams again in an idiot proof form!