Learn English – “meant” and “mean” do both words have the same meaning

The construction would had doesn't exist in English. If you are talking about something that you might do in certain circumstances, you would say:

I would go (if I had the time).

If you are talking about something that you might have done in the past under certain circumstances, you would say:

I would have gone (if I'd had the time).

Neither If I would had been president nor If I would have been president is correct.

To say:

If I had been president

is to reflect on what might have happened in the past if you had occupied the position of president.

To say:

If I were president

is to reflect on what you might do or say in the event that you became president.

The website vocabulary.com says that extended means:

extended (adj.) beyond the literal or primary sense

So I suppose there are two ways a word could have an extended meaning:

• the word could be used in a figurative sense, rather than a literal sense
• the word could have a secondary meaning that we don’t immediately associate with the word

As for your exercise, the word mouth seems easy. People have a mouth, and so od lions – but rivers have a mouth as well.

The mouth of the Rhine is at Hoek van Holland by the North Sea.

As for a word like angry, we only need to consult a good dictionary for ideas. From Wordnik:

angry (adj.)

1. adj. Displaying or feeling anger.
2. Inflamed and painful.
3. Dark and stormy, menacing.

That third one looks like an extended meaning to me. So, we might say:

When Stella noticed the angry clouds, she called her children inside.

The word train has dozens of meanings, so it’s a little harder to figure out which ones are the “primary” definitions and which might the “extended” meanings. But I will say this about the noun train: a railroad yard has a train, but so does a wedding dress. Moreover, about the verb train: a woman might train a dolphin, but she also might train her hair.