SharePoint lists have a default limit of 5,000 items per view. But lists can contain 30 million items (just not all available in one view). Since you’re reading this, perhaps you’ve already learned this from an error message such as:
The view cannot be displayed because it exceeds the list view threshold (5000 items) enforced by the administrator.
To view items, try selecting another view or creating a new view. If you do not have sufficient permissions to create views for this list, ask your administrator to modify the view so that it conforms to the list view threshold.
First of all, when in doubt, refer to the documentation provided by Microsoft. Read it carefully to understand limitations in your specific environment, explanations of various actions and rules and the permissions required to correct the issue.
Here’s my summarized version: