Etimated Position
The RYA Chart is not to be used for navigation, chart 1 has a couple of islands scanned in from the Clyde and the second chart has had the UK moved to the right by about 60nM as well as the Cherbourg peninsular shortened.
The Yellow parts are always land The Green parts are sometimes land and sometimes water The Blue and White parts are always water All the numbers on the chart represent the depth of the water at a very low tide (about the lowest it will get) and is called CHART DATUM, all tide heights are measured from this.
All heights on the yellow parts are measured from the average (mean) high water high (spring) tides this is handy if you are going under a bridge!

Latitude and Longitude

The world is divided up in a form of grid with Latitude and Longitude so we cam pin point any place on the globe. Latitude is measured up and down (North and South) from the Equator from 000 Degrees to 090 Degrees. Latitude is always on the side of the chart and longitude is always on the bottom of the chart. We can only we measure distance from the side of the chart, the lines of latitude are in degrees and there are 360 that circle the globe, these are divided up into 60 sections which are called minutes which are nautical miles. If you were to travel 60 miles north or south then you would have traveled a degree of latitude on your chart!

You will find chart symbols in the document Admiralty Symbols and Abbreviations 5011 there are examples of these in the two books you have.

(A) Try and find the features at the following places
50 20'.45N 004 26'.0W
50 22'.05N 004 30'.0W
50 10'.25N 004 24'5W

Using your Portland Plotter

This is used for measuring bearings between two points or putting a course on the chart. To use the plotter put it on the chart make sure the small green arrows on the central section point to the top and the large green arrows on the plotter point to the place you are going (or the bearing you are taking).
TIP: To make a position line put your pencil on the point and rotate the plotter around it.