Being bilingual generally helps you learn other languages, although not in all cases. Many studies of people who grew up speaking two languages have found that they are often better at learning other languages than people how grew up with just one language. This advantage does depend a number of factors though. For example, if one of the languages spoken by bilinguals is a minority language without official status or support, they tend to perform as well as monolinguals but not better, and if the bilinguals are literate in one of their languages but not the other, they will not have noticeable advantages when learning new languages.
So does this mean that the more languages you learn, the easier it gets? Perhaps – at least some aspects of the process become easier anyway. By learning different languages you become accustomed to different ways of putting sentences together, different ways of marking the relationships between words, different sounds and intonation patterns, and different ways of thinking. These all help when learning new languages. You will probably also develop strategies for learning vocabulary and grammar, and for paraphrasing and generally communicating with whatever words you can remember.
No matter how many languages you know however, it still takes time to acquire vocabulary and to become proficient at using grammar. If you learn languages related to ones you already know, there will probably be plenty familiar words, and the more languages you learn from a particular family, the easier it becomes to recognise such cognates. For example, if you know French and Spanish, you’ll probably be able to understand quite a lot of Portuguese, Italian and other Romance languages.