Purpose
What is someone trying to achieve by doing this?
Meaning
Purpose links an action to what someone wants to achieve by doing it. The intended result may or may not happen. Languages can use special words, verb forms, or endings, while some rely on context without a separate purpose marker. Unlike Cause, Purpose looks ahead to a goal rather than explaining what led to the action.
How to spot it
Find the part that answers what someone does the action to achieve, whether or not that goal is reached.
In your native language
English often uses to followed by the base form of a verb, its form without endings, to show the purpose of an action. So that introduces a purpose with its own subject and often a verb such as can or could. For followed by a noun can show what something is intended for, as in money for lunch.
I went to the library to study.
The same person goes to the library and studies.
I'll leave the key here so that you can get in.
So that allows a different subject: I leave the key, and you get in.
This bag is for wet clothes.
For followed by a noun phrase shows the bag's intended use.
In your learning language
Spanish commonly uses para followed by an infinitive, a verb form such as comprar, when the same person performs the action and its intended purpose. Para que introduces a full purpose clause, often with a different subject. Its verb takes the subjunctive (subjuntivo), a verb form that here presents the outcome as intended rather than as a fact.
Fui al mercado para comprar fruta.
I went to the market to buy fruit.
The same person goes to the market and intends to buy fruit.
Te dejo la llave para que puedas entrar.
I'm leaving you the key so you can get in.
Puedas is subjunctive; the intended action belongs to the listener.
Habla más despacio para que todos te entiendan.
Speak more slowly so everyone can understand you.
Learners whose language uses ordinary statement forms after a purpose word may write *para que puedes entrar instead of para que puedas entrar. Learners whose language uses one marker for causes and goals may use por instead of para.