There are 4 main parties in the Scottish Parliament
1) The Scottish National Party who advocate for independence and broadly centre left policy. They have right wing elements.
They have been in power for 17 years, and currently hold 63/127 seats in Holyrood.
2) The Scottish Green Party, who are quite small, but were in coalition with the SNP in power, creating a majority government at the time.
3) The Scottish Conservatives, who are associated with the UK Conservative Party
4) Scottish Labour who are affiliated to the UK Labour. They are currently surging in the polls for the Scottish election, translating from their overwhelming success in the UK national election campaign.
There are other small parties, such as the Liberal Democrats and the Alba Party.
For the past 3 years, the Green Party and the SNP were in a coalition government. This was enforced by a cooperation agreement called the Bute House Agreement, which, amongst other things, laid out policy areas which the parties did not agree on, such as aviation policy and Scotland's status in NATO.
Last month, Scottish First Minister at the time, Humza Yousaf, terminated the Bute House Agreement, after introducing bills limiting trans rights and extending the net 0 target, which the Green Party disagreed with. This led to no confidence votes in his power from both the SNP and the Conservative Party; which the Green Party supported; leading to his resignation. In the media, the Greens disavowed the decision to end the agreement, describing it as 'political cowardice' with the SNP 'selling out on future generations'.