There are different levels of fluency in any language. Memrise only helps building a serious collection of vocabulary and it's absolutely necessary.
You need around 5000 words to be casually fluent, that is like a native speaker with low education. You'll be able to get around.
To become fully fluent it takes to live speaking solely the language you are learning with natives of that language. I am French and I have been living in the U.S.A. for 23 years. I speak American better than most native and I consider myself fully fluent yet after all this time there are still many words I have never heard for many reasons...technical, not used in the region I live in, specialized, etc.
My estimate is that once you know a language (or think you do) and move to a country where people speak that language it takes around a year or two to become really fluent and for the many years following people will still sometimes smile or laugh at your mistakes.
Well there's still a lot to learn more than vocabulary including the obvious like grammar and idioms. There are different ways of saying things like in German you would say "I am waiting on Bob" but in English it is "I am waiting for Bob". French has the same issues so an English person would sound ridiculous if they directly translate English convention using French words, ie don't say "I am hot" for feeling hot, you'll get some giggles.
But I do think building an extensive vocabulary is the toughest part of gaining fluency, the part that Memrise is best in aiding. So continue using Memrise and pick up a grammar book to get a better picture of the language.