Simple Words - GCIG GNYIS GSUM

Usually it's good to learn the numbers 1, 2, 3 in any language.

gcig - one, but it could be used in any context defining unity, the one and only, singular, complete whole. Sanskrit one is eka, by the way.
Examples:
skyabs gcig - only refuge
ro gcig - one taste (sometimes used as an expression of being inseparable from)

gnyis - two, also means duality, both, either one, dichotomy, two aspects. In Sanskrit this is dva.
Examples:
bden gnyis
- the two truths.
skad gnyis pa -- this is a funny one (!), means having two voices, either a translator (knows two languages), or a parrot.

gsum - three. In Sanskrit, tri.
Examples:
kham gsum
- the three realms (form, formless, desire)
dus gsum - the three times, past, present and future, Buddhas could dwell in the three times, for example. So by now you should be able to translate dus gsum sangs rgyas thams cad.