as a conjunction, 'so that' is used to introduce a clause which indicates the purpose or reason for an action. It can express both purpose (why something is done) and result (what happens because something was done).
'so that' is often used to explain why an action was taken or to indicate the intended result of an action. It can be used in both positive and negative contexts.
She woke up early so that she wouldn't miss the train.
I wear glasses so that I can see clearly.
He whispered so that only I could hear him.
sometimes, 'so' alone can be used in place of 'so that,' especially in informal speech. For example, 'I study hard so I can pass' is equivalent to 'I study hard so that I can pass.' It's important not to confuse 'so that' with 'so' used as a conjunction of result. For instance, 'He was tired, so he went to bed' (result) vs. 'He went to bed early so that he could wake up refreshed' (purpose). In some contexts, especially when the meaning is clear, 'that' can be omitted, but this is more informal
'She closed the door so (that) the cat wouldn't escape.'