Learn Hardcore Swahili: Geuka kushoto kwenye kona ndogo, halafu uvuke daraja. - Turn left at the small corner, then cross the bridge.

geuka = turn (your body/heading) by itself; intransitive. Common in walking directions, and acceptable in driving directions too.
pinda = bend/turn (a vehicle or your path). Very common in road directions: pinda kushoto/kulia.
geuza = turn something (transitive), e.g., geuza gari (turn the car around).
geukia = turn toward someone/something, e.g., geukia mlango (turn toward the door).

Your sentence with pinda is also natural: Pinda kushoto kwenye kona ndogo, halafu vuka/uvuke daraja.

What exactly is kushoto? Is the ku- an infinitive marker?

Here kushoto is not a verb; it’s a locative noun/adverb meaning on/to the left. The initial ku- is part of the word, not the verb infinitive marker. Its counterpart is kulia (on/to the right).

You can also say:

upande wa kushoto = the left side
kushoto kwa X = to the left of X (e.g., kushoto kwa duka = to the left of the shop)

Is kulia (right) the same word as the verb kulia (to cry)? How do people tell them apart?

They’re spelled the same, but context and pronunciation separate them:

kulia (right) is a locative noun/adverb.
kulia (to cry) is a verb from the root -lia. In directions, after verbs like geuka/pinda, kulia clearly means to the right.

Why do we need kwenye before kona ndogo? Could I use katika or leave it out?

kwenye is a very common general preposition for at/in/on a location. kwenye kona ndogo = at the small corner/bend.
katika is more formal/literary but fine here: katika kona ndogo.
Leaving it out sounds odd: geuka kushoto kona ndogo is not idiomatic.
You could also use pale (there) for a known spot: pale kwenye kona ndogo.

Why is it ndogo after kona? Why not kidogo or mdogo?

kona is a class 9/10 noun. The adjective for small that agrees with class 9/10 is ndogo (same form in singular and plural).
kidogo usually means a little/a small amount, or agrees with class 7/8 nouns (e.g., kikombe kidogo).
mdogo agrees with class 1/2 (people/animates), e.g., mtoto mdogo.

Why uvuke instead of vuka after halafu? Are both correct?

Both are correct:

vuka (bare imperative 2sg) is the direct command: Halafu vuka daraja.
uvuke is the 2sg subjunctive (u- + -e). It often feels a bit softer and is common after sequence markers like halafu/kisha to mean and then (you should) cross.

How do I address more than one person?

Two options:

Bare imperatives (plural add -ni): Geukeni kushoto ..., halafu vukeni daraja.
Subjunctive with plural subject prefix m-: Mgeuke kushoto ..., halafu mvuke daraja.

Both are fine; subjunctive often sounds a touch more polite.

How do I make these instructions negative?

Use the negative imperative with the subjunctive:

Singular: Usigeuke kushoto ..., halafu usivuke daraja.
Plural: Msigeuke kushoto ..., halafu msivuke daraja.

Pattern: (u-/m-) + si + verb + -e.

Is a comma before halafu required?

No. You can write either:

Geuka ... kona ndogo, halafu uvuke ...
Geuka ... kona ndogo. Halafu uvuke ... Both are acceptable; it’s a style choice.

Is uvuke daraja the right way to say cross the bridge? Do I need juu ya?

Yes, vuka/uvuke daraja is standard for cross the bridge.

juu ya daraja means on top of the bridge. You could say tembea juu ya daraja (walk on the bridge).
To say via the bridge/using the bridge, you can also use kupitia daraja.
The locative darajani means on/at the bridge.

What are the plurals of daraja and kona?

daraja (class 5) → madaraja (class 6).
kona is class 9/10 and does not change in the plural: kona (sg) → kona (pl). The adjective stays ndogo in both numbers: kona ndogo (sg/pl).

Can I move the location phrase around? For example, can I say Kwenye kona ndogo geuka kushoto?

Yes. All of these are natural, with slight differences in emphasis:

Geuka kushoto kwenye kona ndogo.
Kwenye kona ndogo, geuka kushoto.
Geuka kwenye kona ndogo kushoto. (less common but acceptable)

Is kona ndogo idiomatic? I often hear kona kali or geuka kidogo kushoto.

kona ndogo literally means a small corner/bend and is understandable, though in road talk you more often hear:
- kona kali = a sharp bend
- kona kubwa = a big/wide bend
If you mean slightly left, say geuka/pinda kidogo kushoto (turn a little to the left).
nyembamba means narrow and fits roads, not corners: barabara nyembamba (a narrow road).

Any quick pronunciation tips?

geuka: every vowel is pronounced; it’s ge-u-ka, stress on the second-to-last syllable: ge-U-ka.
kwenye: ny is the single sound [ɲ], like the ñ in Spanish niño: kwe-ɲe.
uvuke: u-VU-ke; stress on VU.
daraja: da-RA-ja; the r is a tap; j as in judge.
kushoto: ku-SHO-to; sh as in ship.

Are there alternatives to halafu?

Yes:

kisha = then/and then (a bit more formal than halafu)
baadaye = later (in time), not just the next step Colloquial spelling alafu is common in speech, but standard writing is halafu.

How do I say at the small corner of the street or to the left of the street?

kwenye kona ndogo ya barabara = at the small corner of the street.
kushoto kwa barabara = to the left of the street.
With a specific landmark: Geuka kushoto pale kwenye kona ndogo ya duka la dawa (turn left there at the small corner by the pharmacy).

When would geuka not be appropriate?

For turning an object/vehicle, use geuza (transitive): Geuza gari (turn the car around).
In many driving instructions, pinda sounds most idiomatic: Pinda kushoto/kulia.
Note: geuka can also mean become/turn into in other contexts: Amegeuka kiongozi (he has become a leader). Context removes ambiguity in directions.