Below is how I understood the questions and how i filled up my application form.
6.4.2 When did you first meet your sponsor?
==> If you met online then indicate the date as to when it happened. and aside from the online meeting, it would be better to also indicated when you first met your sponsor in person (proof of this would be e-ticket, immigration date of arrival stamp in passport, and some photos of you together,etc.)
6.4.3 Where did you first meet?
==> still related to question 6.4.2.
if online, then indicated the website. and aside from that also put in there the place where you actually met in person
6.4.4 When did your relationship begin
==> the answer i placed here was the date when me and my husband first met
6.4.5 How often do you meet?
==> i wrote here 3 weeks every year since we met since my husband comes here in p.i. every year to visit me.