By default, records will open in a side panel on the right of the screen. You also have an option to open records in a modal (pop-up). This can be changed with the following setting:
Portal Tables
Select a table
Views section
In the Default View Settings, change the Open Record as setting.
If your views are set to override default view settings, you'll need to change this setting on a per-view basis, instead of just in the default view settings.