Will I have to fill any application form again to appear for SSC CHSL tier 2 examination?
No, you need not. The staff selection commission, combined higher secondary level exam is an exam with a lot of competition for jobs(LDC/PA/SA/DEO). This exams has three tiers(tier-1:computer based exam,tier-2:descriptive paper,tier-3:typing/skill test)
If yes, than will I have to fill it just after appearing in tier 1 examination or I have to wait till the declaration of tier 1 result?
You have to wait for the result and you be intimated. The SSC releases results and shortlisted candidates on its website. This list will have the full names and the roll numbers. For instance, these two links, are the tier-2 qualified and shortlisted candidates from 2016/17
If you have applied for the SSC-CHSL by the online method in Nov/Dec 2017, you will be completing the tier -1 exams by this month. The results of tier-1 are expected by May 2018. If you are eligible then you will be called for the tier-2 in July. Once you get the results of tier-2 (around October 2018) and qualify (minimum 33%), you will be called for the skill test(Dec2018/Jan20 19).
So, please keep checking the website and the papers around the results time and follow the instruction to get you admit card for tier-2, In the meanwhile please continue your preparation for the tier:2. Please remember that marks from 1&2 have weightage when you come for the skill test.