Learn Russian: Урок начинается утром.

The ending -ся is used for reflexive verbs. Without it, начинает means "starts [something]" (for example, "The teacher starts the lesson"). By adding -ся, the action reflects back onto the subject: Урок начинается simply means "The lesson starts."

Why is "in the morning" translated as just one word, утром, without any prepositions?

Russian often changes the ending of a noun to create a time expression instead of using a preposition like "in". By using a special grammatical form (the instrumental case), the noun утро (morning) becomes утром, which translates to the entire phrase "in the morning."

How is the ending of начинается pronounced?

The letters -тся at the very end of a Russian verb are always pronounced together as -ца (like the "tsa" in "pizza"). You don't pronounce the "т" and "с" as separate sounds.

How would I change this sentence to say "The lesson WILL begin in the morning" using the compound future tense?

To make this future tense, you need the helper verb быть (to be) conjugated to match урок (which acts as a "he/it"), giving us будет. Then, you leave the main verb in its dictionary form (the infinitive), which is начинаться. The future sentence becomes: Урок будет начинаться утром.