There are 120 members in the kenesset, so you need a majority of 61 to have a government. No single party ever had 61 on its own, so the biggest party (usually) forms a coalition with enough other parties to have at least 61 seats.
About 36 parties ran in the election, but only 12 parties got enough votes to get any seats.
To get people to join the coalition, you agree to make concessions in areas that are important to them and to give them Ministries so they have some power besides voting for laws.
If the ruling party tries to pass a law and it fails, its called a vote of no-confidence and the government falls and new elections are required to be schedaled
Opposition has bascially no power at all. Majority can pass any laws they want, but you have to realize because its a coalition not all parties have the same goal.
A simple yet example is the draft. Yesh Atid and Shas might be in the same co-alition. Yesh Atid is for the draft and Shas against.
It isnt as simple as you think, Parties in the ruling coalition have many things in common , but not everything