As mentioned in the previous post there are two types of adjectives, and being able to tell them apart is important as they conjugate differently.
This post will show how to conjugate い-adjectives, which is actually quite easy as it's just changing the ending.
The simplest is the non-past positive version, which is simply the dictionary form of the adjective, for example:
このりんごは美味しいです (This apple is delicious)
Next, we have the non-past negative version, to form this, we take off the final い and add くない, for example:
このりんごは美味しくないです (This apple is not delicious)
Thirdly we have the past positive version, which we form by removing the final い and adding かった, for example:
このりんごは美味しかったです (This apple was delicious)
And lastly we have the past negative, which is formed by removing the final い and adding くなかった, for example:
このりんごは美味しくなかったです (This apple was not delicious)
And that's about it!, there are other things such as the て-form for adjectives, but that'll be covered separately.