Not everywhere in England/Wales has catchment areas
A catchment area is a defined priority admissions area (there will be maps or detailed descriptions). In Scotland, where everywhere has catchments, you are guaranteed a place at your catchment school (but can also request a place elsewhere)
In E/W, living in catchment will give you priority, but it may not guarantee you a place if there are more DC in the catchment than there are places available. Then the tiebreaker is by distance, closer the better. So for example, the entrance criteria will read something like "1) in-catchment with sibling at the school, 2) other catchment children, 3) other siblings, 4) all others"
Otthers have no catchment, and it's all just by distance.
As catchment isn't always sufficient, you probably need also to look at websites (council or school) to establish the admissions footprint (ie how far away do the furthest admitted DC live). So you can see which ones you would have qualified for in the last few years.
You apply through your own council, but can put down schools from the neighbouring one (and they cannot prioritise by borough, just by catchment/distance - councils have well established procedures to co-ordinate)
It is always worth including a school that you're as sure as you can be that you'll get in to, even if you're a bit iffy about it. This is because you are stating preferences, not making a choice, and if your preferences cannot be met, then you will be allocated the nearest school with a vacancy. That might be just as iffy, plus further away.