Only limited people in each Kahootz site can create a workspace. If you don't have the New Workspace link please contact your site owner - they'll be able to help you with your permissions. Your site owner can be contacted through Account > Private Messages > New private message, and picking to: Site owner.
To create a workspace, click on the My Workspaces drop-down at the top of the page and choose New Workspace. The next page will ask you to fill in the basic details of the workspace, such as name and description. The Templates section is where you'll find pre-designed templates, each for different purposes. These can get you off to a quick start by automatically giving you particular sets of teams and content.
If you want to design your own workspace, then you can pick Empty Workspace - that's often the most common route.
If you think your workspace layout and content would be useful in other places in your organisation, ask your site owner to create a new template from it. See more - Workspace Templates.