-니까 gives the reason and 쓰다 is using something. Three lines here use -ㄹ 테니까 in front, meaning 'I'll do my part, so you do yours': I'll fit it now, so try it; I'll send you the link, so try it. Others give permission or refuse it — you're the aunt, so you may; it's a Japanese word, so you shouldn't. This verb also means to write and to wear a hat, but every line here is the 'use' sense.