I am completely new to portals and cannot seem to find much in the way of tutorials
>> You can start by looking at the basic documentation for portals here.
I have created my entity and want to now enter data into it.
How do I create a data entry screen?
>> Data entry in portals is done using the concept of Entity Forms. See documentation here on how to add a form to a web page
Also does the data get saved to the entity?
>> Yes the data gets saved to an entity in Common Data Service (CDS). Having a basic understanding of CDS entities, forms and views will be helpful in ramping up your knowledge in portals
Is it possible to save it to a SharePoint list or is this not recommended.
>> From a portal saving data directly to a SharePoint list may not be straightforward and you'd have to do custom and advanced integration for that. However if data is all you want to read and write from a page then CDS entity forms and entity lists should suffice.