BTech : you would be able to study all the basic concepts related to a field
B Tech + M Tech : basic concepts + research, publish paper in specific area from the vast topics of your field

Dear Sohan,

B-tech is basically a 4 year course where in you take up a broader sector of specialisation and if you intend to do a M-Tech further it would take 2 years and that would be even more particular to the specialisation field. Incase of dual degree the course is for 5 years. The first 4 years are same as B-tech but then the last year will be the specialisation you take up in. The major difference is that in B-tech you have to do a project in your final year with report submission and in dual degree or end of the M-tech 2 year course you have to publish a paper in the project you do. Feel free to as for further clarifications.

All the best!