The installation wizard takes you step-by-step through configuration options and account setup. First, you need to enter the URL of your Nextcloud server. Use for example https://nextcloud.webo.hosting/ (use your correct Nextcloud address, you can find it in Welcome email, this is just an example)
Enter your Nextcloud login on the next screen. (Your username and password used in registration)
On the Local Folder Options screen, you may sync all of your files on the Nextcloud server, or select individual folders. The default local sync folder is Nextcloud, in your home directory. You may change this as well.
When you have completed selecting your sync folders, click the Connect button at the bottom right. The client will attempt to connect to your Nextcloud server, and when it is successful you’ll see two buttons: one to connect to your Nextcloud Web GUI, and one to open your local folder. It will also start synchronizing your files.