Using a PAL for a seven segment display
You need some software (ABEL, WINCUPL, PALASM) and a compatible programmer (hardware). As Bruce says, this series is OTP (one time programmable) so if you make a mistake you need another chip. There were some UV erasable (windowed) parts made with similar capabilities (different part numbers).

You can probably download at least one of the software programs for free, and if you have a universal EPROM programmer that supports PALs you may be all set save for the actual development. The software is so old you may have to run it in emulation under DOS (or equivalent) since it's probably 16-bit code. 

For something more modern, look at Xilinx Coolrunner CPLDs (flash-based) but the software is a bit of a pig.