"I am holding a plate."
Translation:Jag håller i en tallrik.
No significant change in meaning, however, whenever we are holding something in our hands, we usually use the phrase hålla i. It more or less means we are holding on to something.
Note however that if we are holding on to a ledge or other person or something similar, we say hålla tag.
This is a tough one. Tag could be the archaic or formal way of writing the imperative form of the verb att ta, in English to take.
However, in this sentence it acts as a particle to the verb håll, in English hold. Tag as a particle is roughly equivalent to the English [verb] a hold of such as in grab a hold of.
We can use tag as a particle for many things such as:
Håll tag (i) -> Hold on (to)
Fatta tag (om) -> Grab a hold (of)