same here, i pronounced it 100 times and even asked a colleague to pronounce it (he is German native speaker, I work in a German company), he says the voice recognition is wrong, It is first time for me too, it did not happen with other sentence till now. We even tried with sehen, something is definitively wrong with this sentence.
It all depends on the rest of the sentence. A way to know is looking at the verb. There is "sie" which means "she", and the verbs will end in "t" and there is "sie" which means "they" and the verbs end in "en" and last there is "Sie", which means "you (formal)" and also the verbs end in "en". When using the formal word for you (Sie), it is always capitalized.
Surely the use of Sie at the start of a sentance could be interpreted as she or you, and the context of the sentance leads the listener to interpret which is the most appropriate. in mid sentance the use of Sie would be clearly distinguished from sie... but not at the start, where the first letter must be a capital regardless.
They change depending on the case used (nominative, accusative, dative, genitive)
Generally, transitive verbs take an object in accusative (den). That means if you use a verb that does some action with another object/person, this object needs accusative. In this sentence the verb is sehen and the object is der Tisch, it will become den Tisch since it is the receiver of the action of seeing. Things will get more complicated later, but for now take it as a rule. As you master the accusative, any more rules on using the right case will become easier.