the B's and H's..

[She-Wolf]

oh dear, I need to understand about 'bearings' and 'headings' and stuff. I look at the guides as and when I need them, else it doesn't stay in, but on the topic of bearings and headings I THOUGHT I had a basic understanding of sorts - but it seems I don't. We almost came to sharp words last night when best beloved try to explain it to me - so I will ask here instead

Now then. There I am, tootling toward the south, so on a bearing of 180 - or should that be a heading? Then someone yells out that there is a warship closing, bearing 153 ( or something), so I think that means a little to my left, but suddenly a line shoots out from my sub ( this is on the navmap) and points to somewhere way behind me. I query best beloved and HE says something about the bearing being relative to me and that I have to subtract it from the course I am on. Eh? I says - and it goes downhill from there.. so please, to keep the gentle accord we are used to in this little house, will someone please explain in just the smallest and single-worded way possible about b's and h's so that this bear of little brain can understand. Ta