Hello,I am a student and want to know how (or if) to file the obligatory tax filing after 5 years in the country on a student visa. Thanks.

Generally, yes.  If you have income and have met the substantial presence test after your 5 year exemption (based on the visa type) you would then need to file a return to report your income.

Resident alien students

Generally, foreign students in F-1, J-1, or M-1 nonimmigrant status who have been in the United States more than 5 calendar years become resident aliens for U.S. tax purpose if they meet the “Substantial Presence Test” and are liable for Social Security and Medicare taxes. (unless they are exempt from FICA under the "student FICA exemption".

• Student FICA Tax Exemption

Section 3121(b)(10) of the Internal Revenue Code provides another exemption from FICA (Social Security and Medicare) taxes for all students, regardless their U.S. tax residency status. Under this special exception rules, Social Security and Medicare taxes do not apply to services performed by students employed by a school, college, or university where the student enrolled at least half-time. The student’s on-campus employment must be incidental to and for the purpose of pursuing a course of study.  Consequently, a foreign student who become a resident alien may be eligible for exemption if qualified. Off-campus jobs or working for other employers do not qualify.  Revenue Procedure 2005-11 PDF provides instructions for determining who is eligible for the "student FICA exemption."