I was told recently that I can only use the word "too" when it can be
replaced with the word "also". I did not know this. Is that the only time
one can use the word "too"?
Colloquially, we say this:
'I loved that film.'
I wouldn't use 'me also', so while they have a simialr meaning, I don't think that this is a test for whether you can use it. Furthermore, 'too' has other uses, like 'too big'.