Using Streetmap to show an exact location
You are likely to have started from a link to streetmap with an approximate location e.g. from the church database. If the place you are looking for is not on the map, you can use the arrows at the edge of the map to pan up, down, left or right. If the place is a little further away, then use the zoom controls in the bottom right corner of the map to change the scale. Then click on the map at the point you want to show. A new map will be drawn with the point you selected in the middle portion of the screen. Then use the zoom controls again to get back to the larger scale view.
The place you want will probably be visible now, so click on the map at the exact point you want, and a new screen will be displayed with the arrow pointing there. This should be what you want somebody else to see, and the information you need to pass on is the URL shown at the top of your browser window.
Now paste that into an email, and the recipient can click on it to open it up in their web browser to see exactly the same map as you, with the yellow arrow in the same position. Don't use the link at the bottom of this page, as that is there for reporting errors in this page itself.
For those of you who are technically minded and want to extract the exact Ordnance Survey grid reference of the place to which the arrow is pointing, take a look at the instructions for doing that.