What actually happens when you sell, in order.

Seven stages, start to keys.

There are no timescales on this list on purpose. Every honest answer to "how long does it take" is a range so wide it is useless, and a confident number would be the least reliable thing on this site.

1. You find out what it is worth It is free and it commits you to nothing. Two or three opinions is normal, and no reasonable agent will be offended by it. Sold prices near you are public and free to look up, so you can walk into the first appointment already knowing roughly where you stand.
2. You choose who is selling it This is the decision everything else hangs off. Take longer over it than feels necessary, and ask each agent to show you the sold homes their figure is built on.
3. You agree the price, the fee and the length of the contract All three in writing, before anything goes live.
4. It goes on the market and the viewings start Ask who is doing them. It should be somebody who has actually been inside your house.
5. An offer arrives and gets checked A good agent finds out whether that buyer can genuinely proceed before you take the house off the market.
6. Solicitors, searches and surveys Your solicitor sends you forms to fill in about the house and about what you are leaving behind. The buyer's solicitor reads them and sends questions back. Searches go off to the council and the water company. If the buyer is borrowing, their lender will want the house valued, and they may pay for a survey of their own. It goes quiet in places, and quiet here is normal rather than a sign something has gone wrong. A decent agent spends that time chasing everybody involved so that you are not the one doing it.
7. Exchange, then completion Contracts become binding, then the keys change hands, and it is done.

Nothing on that list requires you to have chosen an agent yet.