Assuming that you are flying a cross-country on a defined route, e.g. from A to B or from A to D via B & C this is how to do it.
Choose the "Narrow Route Briefing"
The yellow tinted fields are mandatory and must have something entered in them.
Briefing ID - anything you like, it's for your own reference. The brief will be stored in the "Briefing Handbook" under this ID so you can re-use it if you want.
Date/time of flight - update to reflect when you intend to fly. Date is in ICAO flight plan formant, yymmdd
Departure/Arrival aerodromes, use the ICAO 4 letter designator, if you don't know what it is, it is listed on the frequency card that comes with the CAA charts, in the frequency table on the left hand side of your chart, or you can look it up using the down arrow button on the form. Having found it, you can click the pointing hand at the left hand side of the search result and it will insert the code into the form for you.
Consult the FAQ if either your departure or arrival a/d do not have an ICAO designator. AIS have created dummy designators for a number of such sites.
Traffic - defaults to IFR/VFR. If you are flying VFR changing it to VFR will reduce the amount of data returned.
FL - enter your intended height as a Flight Level, You will get NOTAM from Surface to 4000 ft above this FL for the climb and descent legs, if you have a cruise leg you will get FL+/-4000 ft on the cruise leg. As you are likely to be below 4000 ft VFR this is unlikely to make much difference.
Route - default is DCT. (Direct) If you have turning points enter them using the same syntax you would use for a Flight Plan (e.g. DCT SAM DCT if your turning point was the SAM VOR) As in a Flight Plan, you cannot use an ICAO aerodrome designator as a turning point so EGTT (Southampton) is not allowed but SAM is. You can also use bearing and distance from a navaid - consult the FAQ for how to do this.
Alternate Aerodromes - yopu will get NOTAM affecting the ATZ of any aerodromes you enter here.
What you have done is to create a route 10 NM wide. If it was a straight A to B flight that's a 10 mile wide rectangle plus the 2 mile radius ATZ's at both ends.
Every NOTAM has a geographic centre, a radius of influence, and a height band affected. Something like a flying display might have a 2 mile radius and a height band form SFC to 5000 ft. On the other hand a long-range VOR could have a radius of 250 nm and affect all heights.
You will get everything where the radius of influence touches or cuts your 10 mile wide route, and where any part of the height band affected falls within your FL +/- 4000 ft.
Another option is to choose the VFR FIR and Aerodrome Briefs (assuming you are flying VFR) The aerodrome brief is sorted by aerodrome name and the FIR brief has a North-South sort to help you locate things that may affect you. Read the brief carefully so you understand how the sort works.
Hope this is helpful
Mike