Hi ritika
Some DU Colleges offers various additional courses that can be pursue simultaneously along with your graduation.
The admission in these courses are offline based you hv to go to the college you wish to join the course in and they provide you information regarding the course there itself.
In case you want to do some language or additional course from St Stephens then they do it by online mode and the classes are offered there both on regular days as well as weekends.
Hope that's helpful.