An each-way bet, or ‘ew bet, is two bets: one bet for the selection to win and one bet for the selection to place. The place part of your bet will be settled in accordance with the place terms stated for the event. So if you say “I had a £10 each-way on that winning horse” it means you had a £10 win bet and also a £10 place bet on that winning horse. You staked a total of £20.
If your unit stake is 10 (say £10, if that is the currency of your betting account) then you are placing £10 to win and £10 to place at the relevant place terms for the event.
The payout for placed selections could be for 1st & 2nd or 1st, 2nd & 3rd or for the first four places, depending on the event. Place terms are stated on the sporting event in question. If the each-way option is not showing this is probably because the event you wish to bet on is ‘win only’ and each-way bets are not allowed.