my laptop storage

Service manual and specifications here:

https://www.dell.com/support/home/en-us/product-support/product/g-series-15-5500-laptop/docs

You can add another drive - - however, mounting hardware is required that may or may not be present in the system.  You'll want to remove the base cover to check.

If the hardware isn't present, you'll need to order that from Dell.

Hi @JulesRizk  welcome to this user to user forum. This is not Dell Support. 

Your Dell G5 15 5500 Setup and Specifications > Specifications of Dell G5 15 5500 > Storage options are in this list. Table 1 says that your system's disk interfaces are SATA III and M.2 PCIe Gen3 x4 NVMe. 

Press and hold down the F2 key during boot to enter the BIOS. Look at the bottom of the Main tab and you will see what disks are installed in your system. In the following generic image, your BIOS will have a disk entry that replaces None, and give a brief description of its identity. Your BIOS is generic, so your system may only have provision to install one HDD and two M.2 disks. 

Having booted your system, type System Information into Search (bottom left hand corner of screen) and click on open. Navigate to System Summary > Components > Storage > Disks to see which disk model is listed and installed in your system. Use this information to search on the internet to get the disk's specification. 

This answers your original question of what storage disks are installed in your system and storage upgradability options. Your subsequent selection of storage options should match how you want to use your Dell G5 15 5500. 

Please share an update. Thank you.