Create Domain

Attribute domains are rules that describe the legal values of a field type. Multiple feature classes and tables can share attribute domains stored in the database. However, not all the objects in a feature class or table need to share the same attribute domains.

Step 1- 
 ArcToolbox - Data Management Tools - Domains - Create Domain

Step 2 - 

Step 3 -

Assign your geodatabase as the "Input Workspace"

Step 4 - 

select "Text" as the field type and leave the optional fields at it is. 

Step 5 - 

Then Select the feature class you need- right click- properties 

Step 6 -

Select the field needed to be connect the the domain, then in the field properties select the domain you have created.

Step 7 - 
after it select "Subtypes" - select you field- then click "Domain" button

Step 8 -

Step 9 - 

In the "Coded Value" for "code" you have to assign the field value in you layer attribute table and 

in "Description" you can type any description you need

Step 10 - 

Now you can see you earlier values has been replaced by your domain descriptions

Step 11 - 

Otherwise you can assign add new filed and add the descriptions in the domain

Step 12 - 

When you add new field for the type you have to select "Text" the in the field properties 

"Domain" you can select the domain you need.

Step 13- 

Start Edit you layer

Step 14 -

In the attribute table you can use drop down list to select