Exams for competency

Graduate Record Examinations (GRE)–$213
GREs are of two types: General GRE and Subject GRE. Mostly due to the pandemic GRE had been waived off from most schools. However, I am not sure if they will continue to do so. Biology and Chemistry programs generally do not require GRE (neither general nor subject ones). However, the Mathematics and Physics programs might need the former or both of them. Personally, I don't see any advantage of the GRE, rather I think it significantly adds to the monetary load of the student.
You may refer to these links for more information on different schools' requirements for GRE:
TOEFL (Test of English as a Foreign Language)–$195
TOEFL is one of the critical requirements of most the graduate applications, irrespective of the graduate school or program. It can be substituted by two other tests i.e. IELTS and Duolingo English Test. Both of these are valid tests, but you should look out which test is the most accepted one among your shortlisted universities and register accordingly.
TOEFL is an exam that needs NO coaching. The background we have in English at the institute is sufficient to score well on the exam. It has a total mark of 120, where each section consists of 30 marks (Reading, Listening, Speaking, and Writing). Marks >100 is very good and should allow you to apply to nearly all schools in the US. However, look out to the requirement in your graduate school portal. Practicing is the key. There are multiple modules for you to practice over the internet, and you can search for channels with videos through which you can practice.  You can hold discussions among friends and watch-out English series and movies to increase your speaking and listening skills. TOEFL mark serves as a cutoff, so don't be sad if you can't score 120!  
If your TOEFL mark is just less than the program cutoff, mail the program about that, they will consider!