It is helpful to include the OS Grid Reference for the start point of your walk in your description in TRAIL, so that people can find it if they wish to go direct to the start. The Offer of Walk form on this site has a place where you can enter it, and it will then appear in TRAIL, and on the Scheduled Events page.
You can get a GR from a paper map in the traditional way (the scale along the edge of your compass is useful for this), but there is an easier way, using the streetmap.co.uk web site.
Visit that site in your browser, and in the search field where it says “Enter Postcode, Street, Place or Other”, type in the name of the nearest town, or another land feature such as a loch or mountain name – choose something which is likely to be named on the OS map, and click on “Go”.
You will most likely be presented with a list of possible locations, some common names may be found in more than one part of the country, so click on the most appropriate one. A map will open up showing the town or other location, with an orange arrow at the centre of the map. If the start point of your walk is not visible within the boundaries of the map, move the map around either by clicking and dragging, or by clicking on the arrows around the edges, until you can see it.
Now that your start point is visible, click on the button labelled “Move arrow” which you will find to the right of the map, and move the mouse pointer back onto the map (you will see it change to cross-hairs). With the cross-hairs over your start point, click the left mouse button. The orange arrow will move to the spot, and the map will re-centre on it.
Now look below the map, you will see “Click here to convert coordinates” in small print. Click on the word “here”. A new tab (or window) will appear, with the title “Convert/Measure Coordinates”. The item you need is about half-way down, labelled “Nat Grid”. Copy the one with two letters followed by six digits, this is what is required for the Offer of Walk form.