So first of all, Minecraft has a release version. This being 1.10.2 as an example.
You then have forge, that has 2 versions, first is release version (something that will come back to in a second) and a Minecraft release version. Simply match the minecraft release versions together to gain access to forge, you want to use the latest forge that supports your mc version.
Sponge then also has a few version numbers, one of which is a API version number, an example of this would be 7.1.6, ill come back to this number in a second.
Another version number sponge has is the forge version number. Now the forge version number is the minimum version number that the sponge supports of forge, sometimes you will be in a situation where you can not find a sponge forge version number that matchs your forge version number, thats ok, find the two (or one) sponge versions that have the forge version number between the forge version you have and then get the lower number of the two versions.
Sponge as mentioned before has an api version number. And a sponge plugin will state that it supports a particular api version (or multiple). Match these numbers together to find the supported plugins for your server.
Thanks to sponge being somewhat backwards compatible, if the api version number of the sponge you have is greater then the plugin you want, there is a chance of it being able to run. To find out, get the first number of both the sponge api version and the plugins supported sponge api version and see if they match. For example.
If i had a sponge api version number of 7.1 i could run plugins that have the api version of 7.1 and 7.0 however I could not run plugins that have the api version of 6.1 (because the first numbers dont match) nor 7.2 (because the plugin api version is greater then the sponge api version).
Sponge will also have a few other version numbers attached to them such as sponge common version number and “sponge forge”/“sponge vanilla” version number. In most cases this doesnt matter as most sponge plugins attach to sponge api.
As for your question is sponge version and sponge api version the same. In the example you gave yes, however sponge api is a part of sponge so a sponge version could relate to any part of the sponge system, however most of the time its the sponge api that is mentioned.
The sponge api version that is for 1.10.2 is API 6 I believe however im not 100% sure, thankfully you can go to sponge downloads and filter by mc version.
I believe i have answered all your questions, but if i did miss one or multiple or you just have more please ask/quote yourself more then happy to answer questions