Nouns (名詞) do not take suffixes in Japanese. They don't often take prefixes either. Rather, they are followed by postpositions (like prepositions e.g. to, for, with, against, in, on, at, by, near, around, etc., but after the noun rather than before). They don't change when they are plural e.g. dog and dogs are both inu in Japanese.
As mentioned earlier, Japanese nouns are followed by postpositions. There are lots of these. One of the most common postpositions is wo (pronounced o). This marks the object of a sentence. Thus, in I ate a sandwich, sandwich would be followed by wo because it's the object of the sentence (the thing to which the action is done). Indeed, when translated, the sentence becomes (this is written in Romaji, for ease of use)watashi wa sandoichi wo tabemashita. Other common postpositions include ga (the subject/ doer of the action), ni (when or where an action occurs), and to (and or with). For a more comprehensive list, see Here.
One of the most important postpositions was omitted above due to its complex interactions with fellow particles. It is the particle wa, written as ha. It marks the topic of a sentence, and can therefore not appear with more than one noun. It normally follows other particles, but will replace ga and wo.
For more particles, see particles .