Each voter gets say (for example) 1,000 votes, which they allocate to whichever parties they want at election time.
The number of votes a party gets become its “currency”.
Any political party can put forward legislation to become law. They back their legislation with some number of their votes/currency.
Other parties can defeat legislation by spending a greater number of their votes to stop it.
When a party has spent all its votes/currency, it must wait till the next election to get more.