1.- Store files
We start with the obvious and obvious, but no less important, the ability to store files. The internal memories of some smartphones are of low capacity. There are even 8 GB, although in general today it is no longer uncommon for them to be 16 GB. At best they are 32GB. But if we take into account that the cameras are getting better and better, with higher resolution sensors, and that they record in 4K, we realize that the files they capture are also of high quality and that they weigh a lot. These can be stored on the micro SD card to save space in the internal memory. Just as a camera requires an SD card, and in many cases the photographer has to carry several with him due to the number of photos he shoots, we cannot go thinking about how much space we occupy of the internal memory of the mobile when we shoot photos of the quality that mobile phones offer us today. It is necessary to store the photos and videos on the SD card. Logically, the same happens with music.
2.- Store apps
For a long time Android includes an option with which it is possible to transfer the data from an app to the micro SD card. The app itself must be in the internal memory of the smartphone in order to run, but the data in this app does not have to. And they can be stored on the micro SD card, thus saving internal memory space. For this, you have to go to Settings> Applications, select the app you want and click on Go to SD card, or an option with a similar name.
3.- Use as internal memory
One of the novelties of Android 5.0 Marshmallow is the possibility of using micro SD memory cards as internal memory units. Attention, because not all mobiles have this possibility, despite having Marshmallow, as is the case with the Samsung Galaxy S7, for example. But in general any mobile with the new version should give us this option. In order to use a micro SD card as internal memory you must go to Settings> Storage and USB, and here select the micro SD card. Then click on Options, which will appear in the upper right corner, and select Format as internal. Of course, one thing must be taken into account. Internal memory will almost always be faster than micro SD memory. That is why the faster the card the better. We are not only talking about Class 10, but also about the possibility of buying a card with higher read and write speeds.
Now we can use the micro SD card as if it were internal memory. Of course, we will have to transfer the apps to the micro SD card as in the previous step. The processor is very similar, because you have to go to Settings> Applications, select the app you want, and here select the Memory option. We will see if it is in the internal memory or in the SD memory, and we can click on Change, to switch from one to the other. Bear in mind, of course, that it is possible that the SD apps run somewhat slower, so perhaps a game that we want to play a lot and that requires a high level of processing would be better to leave it in internal memory.