In literal terms, a platform is something people stand on, or things are built on.
In this sense, it is probably used in the software sense. A platform is usually a program, or set of programs, that other programs can be based on, or run on.
You could say that the operating system of a computer or phone is a platform, as apps and programs run on it.
In your sentence, it is probably referring to a social media program, which is sometimes not so much a platform in the more technical sense, but it can be. e.g. Facebook has various apps and games that run on it.
"I think that Android is a good platform. I like the fact that is more open for developers"