So is often used as a general purpose connector and comes at the beginning of sentences.

• So, when do you want to move in?
• So, what have you decided?
• So, what do you think we should do next?

So that

This structure is used to show purpose.

• Speak loudly so that we can hear you.
• Work hard so that you will pass.
• We eat so that we may live.
• He hid himself in the bush so that he would not be caught.

So that may also indicate the result.

• He remained still so that people thought that he had died. (= Because he remained still people thought that he had died.)
• She was standing behind the door so that I couldn’t see her face. (= As she was standing behind the door, I couldn’t see her face.)
• He lowered his voice so that no one would hear.
• I will get a map so that we won’t get lost.

For emphatic use

In an informal style, so is used for emphasizing a quality, feeling or amount. So means the same as very in this case. This structure is like an exclamation.

• I am so happy. (How happy I am!)
• She was so angry. (How angry she was!)
• I’m so glad that you still remember my name.
• Thank you so much for coming.

So… that

This structure shows the result. We cannot use a that-clause after very. Instead, we use so…that.

• I was so excited that I couldn’t sleep.
• She was so tired that she couldn’t walk.
• The tea was so hot that I couldn’t drink it.
• The weather was so hot that we didn’t go out.

Note that the same idea can be expressed using the structure too…to.

• I was too excited to sleep.
• She was too tired to walk.
• The tea was too hot to drink.
• The weather was too hot to go out.