Step 1: Tokenization

Computers don't understand words—they only understand numbers. So we need to convert text into numbers. We do this by creating a vocabulary: a list of all words the model knows, where each word gets a unique ID.

For our calculator, the vocabulary might look like:

{ "zero": 0, "one": 1, "two": 2, "three": 3, ... "plus": 12, "minus": 13, ... }

Now we can convert our input:

"two plus three"
 ↓
["two", "plus", "three"]  → split into words
 ↓
[2, 12, 3]                → look up each word's ID

Each word becomes its ID from the vocabulary. The model never sees "two"—it only sees the number 2.