Learn Italian: Mescolo lo zucchero con il cucchiaio. - I stir the sugar with the spoon.

In Italian, masculine nouns that start with z, s + consonant (like st or sp), gn, ps, or pn take the definite article lo instead of il. Since zucchero starts with a z, we use lo.

What is the dictionary form (infinitive) of mescolo, and can it mean anything else besides 'stir'?

The infinitive is mescolare, which is a regular -are verb. Besides 'to stir', it also means 'to mix', 'to blend', or even 'to shuffle' (like a deck of cards).

Why are con and il written as separate words? Don't prepositions usually combine with articles?

While prepositions like a, di, and in always combine with definite articles (forming words like al, del, nel), the preposition con (with) is usually kept separate. You might occasionally see them combined as col (con + il), but writing con il as two separate words is completely correct and very common in modern Italian.

The word cucchiaio looks tricky to say. What sound does the make?