Hi Charity

There are a number of ways that can help in the navigation of activities in topics.

Activities and topics can have restrictions placed on them so they are only visible when specified conditions are met.

There are blocks that can be added to help navigation such as Section Links

Activities such as Book allow navigation between content 

There are also third party course formats plugins that help navigation. For example, format buttons these will need to be tested to see if they are compatible with Totara 

regards