Of - or

The co-ordinating conjunction of establishes a contrast between two or more alternatives.

We eten vanavond spaghetti of rijst.

Tonight we will eat spaghetti or rice.

It is possible to use of repetitively to create a chain and add stress. Note that in writng the o in of then often receives an acute accent. This has the same effect as the construction 'either ... or ...' in English:

Ik wil of gaan tennissen of gaan squashen.

I want to play either tennis or squash.

Formal language uses the construction hetzij... hetzij ... to achieve this effect this effect:

De voorzitter roept de Raad bijeen, hetzij op eigen initiatief, hetzij als gevolg van schriftelijke aanvraag van ten minste drie leden van de Raad.

The chair will summon the Council, either on his (her) own initiative, or as a result of a written request by at least three members of the Council.

Of can also mean 'if/whether', in which case it is a subordinating conjunction . Do not confuse the two different words.