Paris Metro Entrances

No, entrances don't matter. You can get to either platform, following the signs, from any entrance. Exits matter, in the sense that one exit is likely to put you closer to where you want to be, particularly at the big stations.

The "standard" is that the street entrances all go to a mezzanine level where the turnstiles and ticket booth/machines are located. After you pass through the turnstile, there are signs directing you to the platform and line you want, indicated by the end stations of those directions. So at Place Monge, the south bound platform will be marked "Villejuif/Mairie d'Ivry" and the north bound platform will be marked "La Courneuve".

Stacyl,

Hello.

You'll notice a lot of maps on the walls of many metro stations, both where the trains come and go and in the mezzanine levels. Look for maps that show the immediate neighborhood. These will point you to the specific entrance and-or exit you want to use. The entrances for some metro stations are sometimes relatively far from the train platforms. Some metro stations have four or more entrances.

Enjoy Paris! Cheers.

Chatelet has 20 entrances. It doesn't matter which entrance you enter as long as your line is mentioned; they all lead to all platforms. Lots of stations have half a dozen entrances.

It will not make a difference at Place Monge metro station but there are metro stations that have multiple lines and entering through one stairway or another can make a difference for a person like me who hates walking underground. I try to limit my walking in metro stations to times when I have to make a connection so I usually enter stations through the entrance that puts me closest to the line that I plan to take. It's a nothing burger at Place Monge but at some stations it can make a difference. for example, at Gare de Lyon, if you enter the metro on of the stairs on Blvd Diderot, you are are quite close to Line 1 but will have to walk underground for almost two blocks to get to Line 14. Also, on some of the elevated train lines, you could save yourself a bit of walking by using the stairs that lead directly to the side of the platform where the train going in the direction that you are traveling in arrives. Finally, at some stations, some stairways lead to unstaffed entrances where you must buy a ticket from a machine or already have a ticket or a pass to enter.

I know some stations have only 1 entrance then you follow the signs to the correct platform.

A funny note on that; when you get to a platform following the signs look to see if there are more signs for your train on that platform. We got on the wrong train once not being aware of that; we followed the signs down the stairs and there was a platform, a train came and we got on. Wrong train! Turns out we were supposed to walk across the entire length of the platform to some other stairs on the far end leading to the track we wanted.

You go through the turnstyle.
You look at the stop you want.
You look at the direction the stop goes.
If you have to change lines, there are correspondences which are easy to follow.

It doesn't matter which stairs you use, unless you use the "passengers munis avec billets" - that means "if you don't have tickets already".

The advice here is good for Paris and most other European cities. Note however that there are a few cities where some stations are so shallow beneath the ground that a single flight of stairs goes directly from the street onto the platform and so you do need to use a specific entrance for each direction - I've seen this in particular on certain lines in Lyon and Brussels.

And in London, there are 3 cases where there are two separate nearby stations on different lines. Then you do need to find the correct entrance.
The normal advice is not to change trains there as would you need to go out the ticket barrier, along the street and back in another entrance: Paddington, Edgware Road and Hammersmith.
All 3 are shown as two separate dots on the tube map: http://content.tfl.gov.uk/standard-tube-map.pdf

Be aware that at some stops there appear to be two entrances (back-to-back), but one is actually an exit. I have inadvertently gone part way down a staircase before realizing I am actually going in the out.

None of this applies to London or any other city.
It does apply to Paris, however.