GRE

IELTS and TOEFL are language proficiency exams and GRE is competitive exam for Masters in US or Germany.

Dear Steffi, if you check the websites of each of the universities carefully you will know that GRE is not mandatory for students having a prior degree in mathematics. Having said that since requirements and selectivity depends on a particular university alone I will strongly advise you to communicate with the universities directly.
Best Wishes

Dear Zeeshan, the actual conversion for the CGPA lies with the university & none would have the exact idea. Still you may self check it on the website for WES credential evaluation @ http://www.wes.org/students/igpacalc.asp.

Dear Steffi, 2 years is a pretty long time to study GRE & TOEFL as generally the students take 3 to 6 months to prepare & give the tests.
Since you are doing B.Sc which reflects your interest to pursue your Ms in USA BUT, to remind you that US universities would need a 16 years of education background or a US comparable degree to give you admission for their Ms courses.

you need both. IELTS. is a must to prove your English language test. GRE. if the University asks you have to do prove your engineering aptitude

Hi Raghav,
Here are a few links to help you understand about SOP and LOR. There are general formats, samples and even guidelines on how to write one. You could leave a comment on those pages for any further queries as well.
https://studyabroad.shiksha.com/sop-statement-of-purpose-applycontent1701
https://studyabroad.shiksha.com/lor-recommendation-letter-applycontent2702

You have to appear for one of ielts or toefl to enter the boundaries of a country. This is mandatory. Gre is college admission in good ranked college. Not mandatory everywhere.

Dear Zeeshan, Congratulations for keeping a decent Academic profile. Yes there are options in US & UK for sure as there are a lot of universities available. For Germany, which is the hub of Mech Engg, you are expected to have better Academics besides GRE. You may refer to US News.com & DAAD for university shortlisting & check individual websites for more detailing.