That's true so far.
"Sie", however (with uppercase "S") can also mean (formal) "you", and it uses the same conjugation as "they", so:
- Sie liest eine Zeitung. = She reads a newspaper. (liest = 3rd person singular conjugation
- Sie lesen eine Zeitung. = They read a newspaper. or You read a newspaper. (3rd person plural conjugation)
In general, you can't -- and so both translations will be accepted.
If there is a time indicator, that may narrow down the appropriate tense in English:
- Sie liest gerade ein Buch. "She
is readinga book right now."
- Sie liest jeden Abend ein Buch. "She
readsa book every evening."
Since English uses the present simple for habitual or repeated actions, and the present continuous for actions that are taking place at the present moment.
But without context, a sentence such as Sie liest ein Buch. could be either "She is reading a book." or "She reads a book.", and there's basically no way to tell whether one or the other translation would be better. (It could be the answer to "What is she doing right now?" or to "What does she do every evening?", for example.)
Whats the difference between saying "liest" and "lessen"
lessen is not a German word.
The verb lesen (to read) is conjugated like this:
- ich lese (I read)
- du liest (you [one person] read)
- er/sie/es liest (he/she/it reads)
- wir lesen (we read)
- ihr lest (you [several people] read)
- sie lesen (they read) / Sie lesen (you [formal] read)
You have to use the verb form that matches the subject.
Here, the sentence is talking about several people, so you need sie lesen (they read).