If the station is a ChargePoint station, you'll need a ChargePoint card, which you can order at the chargepoint.com website. Same for Blink or any other network, I would imagine.
If you drive up to a station, it should be obviously marked as to which network it belongs to. Also, the stations on each network tend to look a certain way, as they each use a particular EVSE manufacturer. Most ChargePoint stations, for example, have a "square aluminum tube" appearance, usually chest-height. I think the Blink stations (though I haven't used one) are often white boxes. An easier way to determine which kinds of stations are around you, though, is to use the mapping features available via the networks' websites/apps. Or, use a third-party website/app like plugshare.com.
Btw, you'll probably find that a lot of stations are actually free to use, but you just need a membership card to activate them. In the worst case (if you forgot your card or the station isn't recognizing it) you can just call the network up, give them your membership info, and they can remotely activate the station.