Learn French: Moi, j'ai une tablette moderne. - I myself have a modern tablet.

In French, the word je (I) drops its 'e' and uses an apostrophe when the next word starts with a vowel. Since the verb ai (have) starts with an 'a', je ai combines into j'ai. This makes it smoother to pronounce!

Why does the sentence start with Moi if j' already means "I"?

You are right that j' means "I". The word Moi is a stress pronoun used for emphasis. It is like saying "As for me, I have..." or "I myself have...". French speakers use this pattern a lot in everyday conversation to highlight who they are talking about.

Why is the adjective moderne placed after the noun tablette?

In English, we put the adjective before the noun, like "modern tablet". In French, most adjectives are placed exactly the opposite way: right after the noun they describe. That is why it is written as une tablette moderne.

Would the spelling of moderne change if the object were masculine?

No, it would stay exactly the same! Usually, you add an 'e' to a French adjective to make it feminine. But when an adjective's basic masculine form already ends in an 'e', like moderne, it does not take an extra 'e' for feminine words like tablette.