Learn Spanish (Latin America): El campeonato no es tan importante como la competencia. - The championship is not as important as the competition.

We use tan because it comes right before an adjective (importante). If we were comparing nouns, like saying 'as much competition', we would use tanta to match the noun. The formula for adjectives is always tan + adjective + como to mean 'as [adjective] as'.

Does the adjective importante change depending on whether it describes a masculine or feminine word?

No, because importante ends in the letter -e. Adjectives that end in -e or a consonant usually have the same form for both masculine and feminine nouns. If the noun were plural, like los campeonatos, it would become importantes, but the gender does not change it.

What is the exact difference between campeonato and competencia?

Campeonato specifically refers to a championship or a tournament with a final winner. Competencia is a broader word that means competition in general. Note that competencia can also mean competence (having the skill to do something), just like in English!

How does the negative word no change the structure of the comparison?