"I speak a little Esperanto."
Translation:Mi parolas Esperanton iomete.
Esperanta is an adjective, it describes (or "modifies") nouns. For example, you can have esperanta vorto. An Esperanto word. Esperante is an adverb, it modifies verbs, adjectives and even other adverbs. In this case it was in the example because it is modifying the verb "parolas". In the same way that "speaking slowly" is "malrapide parolas", "speaking Esperanto-ly" is "esperante parolas".
There are many ways to say the same things in esperanto due to its simple structure and openness to other languages. The purpose of allowing all these different manners of saying things is so that when speaking esperanto, it hardly feels any different from speaking your mother tongue, no matter what it is (in most cases).
It would be understood if you said it this way even though it is not very natural and it could be interpreted ambiguously.
More natural would be "Mi parolas iom da esperanto". The word "iom" is used to signify a quantity of something and as such it is used often to describe nouns. This could still be interpreted strangely.
I prefer to use "iomete" in these situations so that it isn't assumed I am a fluent speaker who just happens to be speaking only a select amount.