The roles and responsibilities of a Tableau developer depend on what type of project they are working on. But if we generalize it then a Tableau developer has to do the following tasks on day to day basis:-
They need to understand the data and Key performance indicators or views that will be visible on the final dashboard.
They are responsible for creating a wireframe to design documents in order to finalize the number of dashboards and graphs, graph type and color code.
They need to connect Tableau to the database and creating designed dashboards.
They need to test the data quality by comparing the output of the dashboard with the database. Functional testing by checking filters, navigation etc.
They are also responsible for publishing dashboards on the server and giving access to users. Getting reviews from end-users and modifying the dashboards accordingly.
If you want to become a Tableau developer then you must take-up the following Tableau training course. You can also watch the following Tableau video tutorial to learn more about it.