Learn Portuguese (Portugal): Eu acho que é fácil.

In Portuguese, achar is used when expressing an opinion, making a guess, or stating what you reckon. The verb pensar is used more for the actual mental process of pondering. Since this sentence expresses an opinion about something being easy, acho is the correct choice.

Can I drop the word que like we drop 'that' in English?

No. In English, we often say 'I reckon it is easy' instead of 'I reckon that it is easy.' In Portuguese, the connecting word que is practically mandatory to link the two parts of the sentence. You always need to say acho que (I think that).

Why do we use é instead of está for 'it is'?

Portuguese has two verbs for 'to be': ser (for permanent or inherent traits) and estar (for temporary states). If a task or subject is easy (fácil), it is considered a core characteristic of that thing, not a temporary condition. Therefore, we use é, which comes from the verb ser.

Does fácil change depending on whether the thing I am talking about is masculine or feminine?

No. Adjectives that end in the letter L, such as fácil (easy) or difícil (hard), are gender-neutral. They stay exactly the same whether you are describing a masculine noun or a feminine noun.