Here are three parts of Sanskrit that English speakers often find unusual.
Word endings
In Sanskrit, a lot of a word's meaning is in its ending, and changing a word's ending changes its meaning. Sanskrit uses many different kinds of word endings.
For example, the word gajena means "with the elephant," but the word gajeṣu means "among the elephants" instead. Or, the word gacchāmi means "I go," but the word gaccheyuḥ means "they might go" instead.
Word order
Because Sanskrit word endings hold so much information, Sanskrit word order is much more flexible than it is in English.
For example, the sentences "Rama kills Ravana" and "Ravana kills Rama" mean very different things in English. But in Sanskrit, word endings make the meaning clear. rāmo rāvaṇaṃ mārayati and rāvaṇaṃ rāmo mārayati both mean "Rama kills Ravana."
Sound changes
When we speak quickly, we subconsciously make small changes to our speech to make things easier to say. For example, native English speakers will pronounce the word "the" in the phrases "the office" and "the car" in two different ways: thee office compared to thuh car.
This happens in Sanskrit, too. But in Sanskrit, these changes are written down. So, words like rāmo, rāmaḥ, rāmas, and rāmaś all mean the same thing, though they are written and pronounced differently.