If you have a role where you need to know such things someone should be available to ask these questions to. Better to ask even the simple questions at the start than discover you've been getting it wrong months down the line!
ELRs - A unique reference number for a line. Found in the Sectional Appendix. You might hear people say "such-and-such happened and 60 mile 15 chain on the
MLN1". Every place can be uniquely identified by the ELR and mileage.
LOR - A collection of ELRs forming a route. Also found in the Sectional Appendix.
Sectional Appendix - Documents that give lots of information about an area of railway. Some of the information is for drivers and probably not too relevant, but there is also information on possession requirements and the map pages which are very useful and were I'd go for the ELR and LOR (there may be other locations).
https://www.networkrail.co.uk/indus...ators/national-electronic-sectional-appendix/
Hazard Directory - Lists lots of information, including Hazards (buried services, invasive species, restricted clearance areas etc) and Access Points. Best used with local knowledge where possible as it's a bit lacking at times, or very outdated.
I'd also recommend the
NR Jargon Buster and I can recommend
Ellis' British Railway Encyclopaedia for usually having the answer to anything except the most specialised of things, but it's just over £20.