Learn Hardcore German: Der Techniker beginnt seine Schicht um sieben Uhr. - The technician begins his shift at seven o’clock.

Der is the nominative masculine singular definite article. Techniker is a masculine noun meaning technician. Die Techniker would be plural (the technicians). If you wanted an indefinite singular, you’d use ein Techniker.

How would the sentence change if the technician were a woman?

You’d say: Die Technikerin beginnt ihre Schicht um sieben Uhr.

Feminine form of the job: Technikerin
Possessive changes to match a feminine possessor: ihre Schicht (her shift)

Why does it say beginnt? How is beginnen conjugated?

Beginnt is 3rd person singular present of beginnen. Present tense:

ich beginne
du beginnst
er/sie/es beginnt
wir beginnen
ihr beginnt
sie/Sie beginnen

Can I use anfangen or starten instead of beginnen?

anfangen is common and a bit more colloquial. It’s separable: Der Techniker fängt um sieben Uhr an. With an object, both are possible: Er fängt um sieben Uhr mit seiner Schicht an or Er fängt seine Schicht um sieben Uhr an.
starten is used, but sounds more technical or event-like. People do say Er startet um sieben, but for a person’s work shift, beginnen/anfangen is usually preferred. For events or machines, starten is very natural.

Why is it seine Schicht and not sein Schicht or seinen Schicht?

Because Schicht is feminine and is the direct object (accusative). Possessive adjectives agree with the noun they modify:

Feminine accusative singular takes -e → seine Schicht.
sein Schicht would be wrong (no ending).
seinen Schicht uses a masculine accusative ending, so it would only fit a masculine noun (e.g., seinen Arbeitstag).

What case is Schicht in here?

Accusative. Beginnen is transitive and takes a direct object, so (seine) Schicht is in the accusative.

What does um mean in time expressions, and what case does it take?

With clock times, um means at and it takes the accusative. Examples:

um sieben (Uhr) = at seven (o’clock)
um diese Zeit (accusative)
um Mitternacht Note: um also means around in spatial senses (e.g., um den Tisch) and still takes accusative.

Do I have to include Uhr? Is um sieben okay?

Both are correct:

um sieben Uhr is explicit/formal.
um sieben is perfectly natural in everyday speech. For approximate times, use gegen: gegen sieben (Uhr) = around seven.

How do I say 7 a.m. vs 7 p.m.?

7 a.m.: um sieben Uhr morgens or simply um sieben Uhr (context often makes it clear).
7 p.m.: um neunzehn Uhr (24‑hour clock) or um sieben Uhr abends.

How would I say 7:30? And what does halb acht mean?

um sieben Uhr dreißig or um halb acht.
In German, halb acht means half to eight (i.e., 7:30), not 8:30.

Can the time phrase move to the start of the sentence?

Yes. German is verb-second:

Um sieben Uhr beginnt der Techniker seine Schicht. You can also put the time mid-sentence:
Der Techniker beginnt um sieben Uhr seine Schicht. Both are natural; placing time first is common for emphasis or flow.

Could I say beginnen mit instead of a direct object?

Yes. Beginnen works both transitively and with mit + dative:

Der Techniker beginnt seine Schicht um sieben Uhr.
Der Techniker beginnt um sieben Uhr mit seiner Schicht. (note the dative: seiner Schicht)

What’s the difference between Schicht, Dienst, and Arbeit here?

Schicht: a shift (typical in shift work like factories, hospitals).
Dienst: duty/shift, common in public service, healthcare, police, etc. Dienstbeginn = start of duty.
Arbeit: work in a general sense. You could also say Er beginnt um sieben Uhr mit der Arbeit, but Schicht pinpoints the scheduled shift.

Any pronunciation tips for Techniker and Uhr?

Techniker: The ch is the “ich-sound” [ç], not like English ch. Stress the first syllable: [ˈtɛç.ni.kɐ].
Uhr: Long u [uː]; roughly like English “oo” in “food,” then a light r: [uːɐ].

Why are Techniker, Schicht, and Uhr capitalized?

All nouns are capitalized in German: Techniker, Schicht, Uhr. Der is capitalized because it starts the sentence; seine is a pronoun and stays lowercase.