Many, if not all, languages have homonyms (омонимы) – words that look and sound the same but have different meanings. Think of 'bow' or 'cool' in English, they too have more than one meaning. Russian is no exception. It might make things confusing even for someone advanced in the language, when you see a word like ручка and don't know if this time it means a handle or a pen. I'll give you some examples of Russian homonyms.
лук — onion; bow (weapon)
мыло — soap; email
ручка — handle; pen
коса — scythe; braid; spit (landform)
косой — cross-eyed; askew, sideways; nickname for a hare
бабочка — butterfly; bow-tie
брак — marriage; spoilage, flaw (in a product)
мир — peace; world; society («Война и мир» - “War and peace” can also be translated from Russian as 'War and society' and 'War and world')
киви — kiwi fruit; kiwi bird
мука — torture (мука — first syllable is stressed); flour (мука — second syllable is stressed)
чайник — teapot, kettle; inexperienced driver, a beginner in general, a dummy (colloquial word).
There are of course many more such words. Don't be afraid to make mistakes with them – it's only natural :). Eventually you'll learn the most common homonyms and will be able to guess the right meaning out of context.
If you are ready for some mind breaking, I give you this:
Косил косой косой косой.
Looks cool, huh? Can you translate it?
I'll help you with the words:
косить — to cut grass
косой — cross-eyed, sideways or a hare
коса — here: scythe, so косой means [doing something] with a scythe
косая коса — askew scythe
A cross-eyed person was cutting grass with an askew scythe.
Or maybe it was a hare cutting grass...