Learn Farsi: تند بدو!

To give a command to one person, we add the prefix be- to the present stem of the verb. The present stem for دویدن (to run) is دو (dou). When we combine them, be- plus dou gives us the imperative بدو (run!).

How is the letter و pronounced in بدو?

In the stem دو, the letter و (vav) acts as a vowel here, making an "ou" or "ow" sound. The whole word is pronounced "bedou".

I learned that تند means "spicy". Why is it translated as "fast" here?

The word تند is used for both "spicy" (when talking about food) and "fast" or "quick" (when describing an action). Since you can't run in a spicy way, it means "fast" in this sentence!

Do I need to include the word for "you" (تو) before telling someone to run?

No, you don't need to. The imperative verb بدو (run!) already has the singular "you" built into it. You could say تو تند بدو if you really wanted to emphasize who should run fast, but usually the pronoun is dropped.