I don't have a perfect translation, but I want to explain what the sentence means (in my opinion). The first part of the sentence states: "It is all not so easy.". You would say it as a kind of sigh before you start a big task and don't know where to begin. Or if you received bad news that something did not work out as it should. So this part of the sentence has something of "Life is not easy!" or something like that. You can say it with a sigh or a shrug.

Then the second part of the sentence follows that takes the weight/resignation off the situation.

"Einfach" means easy or single. So, as stated before, this is also a pun. And it turns the first part of the sentence to a nonsense phrase, saying "Nothing is single, if you take it double". For example, if you use a rope, you can use it in a single way or double (or two ropes). If you use it in a double way, it is no longer single, of course.

So when do you use this sentence? You would use it to express, that you feel a bit resigned, but still have some good faith and can show a smile and don't take things too hard.