1. Role of Keigo
Keigo plays a very important role in building human relationships in Japanese society. Honorific expressions are used differently depending on how close you are to the person, as well as differences in social standing such as age, status, and experience. Honorific language is polite language, and communication goes better when you use honorific language. On the other hand, when honorific language is used, you may feel a distance. Depending on your familiarity with person, you need to use them differently.

2. Examples
いる　ー　いらっしゃる　ー　おる

行く　ー　いらっしゃる　ー　参る/うかがう


食べる　ー　召し上がる　ー　いただく

する　ー　なさる　ー　いたす

3. Basics of how to use honorifics
Basics Keigo is used for SOTO people in your group. We use difficult honorific language to refer to people from SOTO, and humble language to refer to people from home. For example, when speaking on the phone, we use different honorific expressions, such as:

Asahi:「恐れ入りますが、営業部のマリナ課長がいらっしゃいますでしょうか。」
Sapporo:「あいにく、マリナは、ただ今、外出しております。』

For Sapporo Marina is from another company, meaning SOTO, so the honorific title マリナ課長 was used. On the other hand, for Asahi Marina is from own company, meaning NAKA, so she is called マリナ without the honorific title.

4. How to add お and ご
Add ご before the kango (words of Chinese origin), and add お before wago (words of Japanese origin). Also, don't put お or ご in front of katakana words.
Example: x ビール, x ジュース

5. Double honorific language
二重敬語
Expressions such as "honorific language(sonkeigo) + honorific language(sonkeigo)" or "humble language(kenjogo) + humble language(kenjogo)" are called 二重敬語(double honorific language). Basically, this is the wrong usage of honorific language.
For example, the expression お召し上がりください is a phrase you often hear, but this is a double honorific, because 召し上がる and お〜ください are both honorifics. The correct honorific expressions for 食べる（召し上がる） are お食べになってください and 召し上がってください.
Although double honorific expressions are considered incorrect in Japanese language tests, there are many expressions that have become established in Japanese conversation (for example お召し上がりください). The double honorific language can be said to be an expression of strong feelings of respect. Let's value our feelings for the other person more than words.

Have you ever heard 二重敬語? Share examples in the comments!