The most important thing in Germany, if you want to survive and thrive, is German Language.
There are 6 different levels of German language.
You can either learn German in Goethe Institut in India (also known as Max Mueller Bhavan) or learn it from private institutes and then give exams conducted by Goethe Institut at the end. The certificate from Goethe Institut is recognized in Germany and is much preferred rather than having a certificates issued by any other private institutes.
The following overview and understanding of German language levels will help you to understand expectations from each level.
A1 and A2: use of language at elementary level.
B1 and B2: use of language independently.
C1 and C2: use of language like a native speaker.
More information on this can be found at this link.
If you are planning for your undergraduate studies in Germany, you need to prepare for TestAS. TestAS was developed by ITB Consulting Bonn and TestDaF Institute Hagen. The project was sponsored by the German Federal Ministry of Education and Research. More information can be found on at these websites: Link 1 Link 2.
German language is not similar to English or any other foreign language as it has own set of grammar rules which one should follow in order to learn the language.
You can practice German for free under this link.
The best way to learn German is with friends through some apps, through listening tosongs, having conversation with a native speaker.