Learn Portuguese (Portugal): Isto é a mesa.

Isto means "this thing". It is a neutral, invariable word, meaning it never changes to match masculine or feminine nouns. We use it to point out a general object before identifying it, like saying "This (thing right here) is the table." If you wanted to say "This table", you would need the feminine word esta, as in esta mesa.

Why use é here instead of está?

The verb ser (which gives us é) is used to identify what something is. Even though a table can be moved around, its core identity as a table is permanent. The other verb for "to be", estar (which gives us está), is used for temporary states or physical locations, not for defining what objects are.

How do we know to use a before mesa?

In Portuguese, all nouns have a gender. Words ending in -a, like mesa, are almost always feminine. Because it is a feminine singular noun, we must use the feminine singular word for "the", which is a.

If the table was far away, would we still use isto?