When we learn a new language as adults, we often struggle with articulating the sounds.
What is relatively easy for children whose palate is still soft, becomes increasingly difficult the older we get. Usually, when children hit puberty, their palate hardens which makes it a bit more difficult for them to articulate new sounds.
Against common assumptions that adults can not become as phonetically fluent as children, it needs to be said that it is possible, if we have the right training and invest enough time to learn.
A simplified cross section that might help to get started:
This interactive IPA chart can help you practice articulating sounds.