Hi Mama,
Unfortunately I don't have a photo tour of Gare de l'Est, nor do I know this station very well.
I'll try my best to help you either way.
When you arrive at Paris Est, you'll need to follow
directional signs towards the Metro like this one. You can take either Metro Line 5, direction Bobigny or Metro Line 4, direction Porte de Clignancourt to go from Gare de l'Est to Gare du Nord, which is only one stop away.
At Paris Est, when you've found the Metro station, the ticket hall should have both a manned ticket window or booth and also ticket vending machines. The ticket vending machines, purple and white colour, operate in both French and English. These machines take Euro coins or European debit cards (
but not North American credit cards). They are operated through a big metal "handle" that turns, which you roll up or down to change the position of the item selected on the video screen of the vending machine. When the selector is on the correct item, press the green button to the right of the handle, which makes your selection. What you're looking to buy is a Ticket t+ Metro ticket. And you'll want to choose just 1 ticket (you'll have the choice of buying 1-10 tickets, and "carnets" or books of 10 or 20). The cost will be €1.60. The machine will ask for a payment type, choose Cash/Coin, which unlocks the coin slot, unless you have a Carte Bleu debit card and wish to use that. The machine will also ask if you want a receipt; Say "Yes" in case you've bought the wrong ticket and want a refund from the ticket window.
Assuming that you've got your ticket in hand, you'll need to find the entrance turnstiles and insert your ticket into the machine, retrieving it from the top after it's been "validated" by the turnstile. The turnstile readout should show "Prenez votre ticket" and the bars or gate should be unlocked and you can pass through. Some turnstiles, which open like elevator doors, can be very slow to open. Simply stand close and wait for the barrier to open, don't back out and try your ticket again, which will fail (tickets cannot be used multiple times for the same entry point).
Make your way to either Metro 4, direction Porte de Clignancourt or Metro 5 direction Bobigny Picasso. Either will work for getting you to Gare du Nord, only one stop away.
Now, as for getting from Paris to London, you need to buy a ticket for the special high speed train known as Eurostar to complete this trip. RER trains only operate within Paris and Ile-de-France. See my article on
Paris to London on Eurostar for information on buying Eurostar tickets and taking the train. Also see the
Gare du Nord photo tour to get your bearings and to help you find the Eurostar level.
Best of luck,
Ben