People don’t always say just one sentence. Lojban has a specific structure for talk or writing that is longer than one sentence. The entirety of a given speech event or written text is called an utterance. The sentences (usually, but not always, bridi) in an utterance are separated by the cmavo “ni'o” and “.i”. These correspond to a brief pause (or nothing at all) in spoken English, and the various punctuation marks like period, question mark, and exclamation mark in written English. These separators prevent the sumti at the beginning of the next sentence from being mistaken for a trailing sumti of the previous sentence.
The cmavo “ni'o” separates paragraphs (covering different topics of discussion). In a long text or utterance, the topical structure of the text may be indicated by multiple “ni'o”s, with perhaps “ni'oni'oni'o” used to indicate a chapter, “ni'oni'o” to indicate a section, and a single “ni'o” to indicate a subtopic corresponding to a single English paragraph.
The cmavo “.i” separates sentences. It is sometimes compounded with words that modify the exact meaning (the semantics) of the sentence in the context of the utterance. (The cmavo “xu”, discussed in Section 15, is one such word — it turns the sentence from a statement to a question about truth.) When more than one person is talking, a new speaker will usually omit the “.i” even though she/he may be continuing on the same topic.
It is still O.K. for a new speaker to say the “.i” before continuing; indeed, it is encouraged for maximum clarity (since it is possible that the second speaker might merely be adding words onto the end of the first speaker’s sentence). A good translation for “.i” is the “and” used in run-on sentences when people are talking informally: “I did this, and then I did that, and ..., and ...”.