No you can take admission through both merit basis and entrance basis. To take admission into courses like B.Sc and B.Sc Hons, B.Com Hons and B.Com, B.A, you don't need to appear for DUET or DU JAT. Apart from these courses you will have to appear for DUET (Delhi University Entrance Test) or DU JAT (Delhi University Joint Admission Test).
To take admission into courses like Bachelor of Management Studies (BMS), BBA FIA (Bachelor of Business Administration Financial Investment Analysis) and B.A. Hons in Business Economics, you Will have to appear for DU JAT.
Application for both DUET and DU JAT have not been released yet. Dates for the application forms have not been as well. But, I am mentioning expected dates for release of both the exams-
1. DUET- 1 st week of May, 2021
2. DU JAT- 3rd week of June, 2021
To see a complete list of all the entrance based and merit based courses of Delhi University, please go through this link