There are a few different versions of the Steam Deck that players can purchase for themselves. The clearest difference between these versions is their storage capacity, which in turn raises each version's price slightly. There's a 64GB, 256GB, and 512GB option when it comes to storage. In modern gaming, 64GB won't be enough to download a single AAA game. While the latter options can hold up to five or six games, sometimes players simply want more access. If players desire more downloaded games, they can purchase and install a microSD card.
A microSD card is a small storage device that's mainly used to store files, such as photographs, videos, and other data. However, gamers can take advantage of this technology to expand their Steam Deck storage. There are several affordable options for players, which vary in storage capacity and read/write times. Some 512GB models from reputable brands can be purchased for under $60, for example.
Once players have determined which price and storage capacity works for them, they can then go on to install the card onto their Steam Deck and format it to hold games. Below, players can find out exactly how to do this.
With the microSD card in hand, find the slot for it on the bottom of the Steam Deck. This is found on the right side of the bottom of the device. Your Steam Deck can be either turned on or off for this process. Make sure to hold the card the correct way; there should be an arrow on the card that indicates which way it needs to be inserted into the slot. As you are inserting the card, they should be putting a solid amount of pressure to make sure it fully goes into the slot. You will know the microSD card is fully inserted if it's not sticking out of the bottom of the Steam
Read more on gamespot.com