1984 plymouth reliant wont start when I turn the key the engine just ticks what might be the problem?

HI, generally a heavy clicking noise from the engine bay when trying to crank indicates the battery is too discharged or worn to engage the starter motor, try a jump start or replacement battery.

Hope this helps,

John

Dirty Battery terminals perhaps clean with terminal clen tool and check battery with volt meter should read 12 volts or better