The exercises in this tutorial take you through 2 easy steps with sample data to build simple mosaic datasets and help you to understand some of the decisions you need to consider for your data and the uses of the mosaic dataset.
Step: 1
Create a file geodatabase
Go to the Catalog button
Opens the Catalog window.
Rightclick and click New Folder.
Name the folder as you wish.
Rightclick your folder and click New File Geodatabase.
Rename the new file geodatabase as you wish.

Step:2 Mosaic dataset and add rasters to the mosaic dataset

Rightclick Geodatabase in the Catalog window and click New Mosaic Dataset.
Open the Create Mosaic Dataset tool dialog box.
Type name as you wish in the Mosaic Dataset Name text box.
Click the Coordinate System browse button Spatial Reference Properties.
Expand Projected Coordinate Systems and select according to your image coordinate system.
Click OK on the Create Mosaic Dataset tool dialog box.

Add rasters to the mosaic dataset

Rightclick your mosaic dataset in the Catalog window and click Add Rasters.
Open the Add Rasters To Mosaic Dataset tool.
In the Raster Type list, choose Raster Dataset.
Click the dropdown arrow and click the dataset.
Click the Input browse button.
Navigate to your file location and click Add.
Check Update Overviews.
Click OK to run the tool.