"-ci" in Turkish means the suffix "-er" in English. We give a duty to someone or something.

yardım (help) | yardım+ci---------->yardımcı (helper)

Size yardımcı olabilir miyim? (Can I be helper to you?)

futbol (football, soccer)

futbol+ci-------------->futbolcu (footballer)

şarkı (song)

şarkı+cı--------------->şarkıcı (singer)

sanat (art)

sanat+cı-------------->sanatçı (artist)

gazete (newspaper)

gazete+ci------------->gazeteci (journalist)

yalan (lie)

yalan+ci--------------->yalancı (liar)

tiyatro (theatre)

tiyatro+ci-------------->tiyatrocu (theatre player)

gitar (guitar)

gitar+ci---------------->gitarcı (guitarist)

kin (grudge, rancour)

kin+ci------------------>kinci (rancorous)

siyaset (politics)

siyaset+ci-------------->siyasetçi (politician)

matematik (maths)

matematik+ci----------->matematikçi (matematician)

ırk (race)

ırk+ci----------------->ırkçı (racist)

din (religion)

din+ci----------------->dinci (bigot, bigoted)

milliyet (nation)

milliyet+ci------------->milliyetçi (nationalist)

etc. etc. etc.

We can also express to be a supporter in politics or sometimes in sport or something like these.

examples in politics:

Atatürk (the founder of the Turkish Republic)

Atatürk+ci------------->Atatürkçü (Kemalist)

Hitler (der Führer)

Hitler+ci--------------->Hitlerci (Hitlerist)

sağ (right)

sağ+ci----------------->sağcı (rightist)

sol (left)

sol+ci------------------>solcu (leftist)

halk (folk, people)

halk+ci----------------->halkçı (populist)

examples in sports:

Schumacher (one of the legend drivers of F1)

Schumacher+ci--------->Schumacherci (fan of Schumacher)

McLaren

McLaren+ci------------->McLarenci (fan of McLaren)

in football or another sports, the suffix is "-li", not "-ci"

Beşiktaş (the oldest football club of Turkey)

Beşiktaş+li-------------->Beşiktaşlı (fan of Beşiktaş)

Liverpool

Liverpool+li-------------->Liverpoollu (fan of Liverpool)

Arsenal

Arsenal+li--------------->Arsenalli (fan of Arsenal)

etc. etc.

This was already very limited topic. Nothing else to explain remained.