In order to receive alerts about data usage, we need to make sure that the first option is activated
It says, "Limit mobile data usage", and the box on the right is green with a checkmark inside it. This function must be activated in order to receive alerts about data usage. To learn how to activate it, search for a video on this website for a tutorial on how to do that.
In the table further down on that menu, we can see there is a data usage limit that has been set
We have set this earlier. Right now, we can see the gray line, and just to the left of it it says, "4.6GB LIMIT". This is the data usage limit that we have set. What we want to do now is to receive an alert when we are close to this limit. This alert will tell us when we are close, so we know we need to change our behavior. We may need to not use internet so much and save that space for emergencies or more important things. Then we won't use all of our data usage without knowing about it.
If we scroll down to the table again, we can now see that there is a new line
It is a line with a little green dot on the end. This is our alert, and currently it is set to 2.8GB. This is what our alert is set to. What that means is when we have used 2.8 Gigabytes of our data usage limit, which is 4.7 total, then we will receive an alert about it. We can edit and customize when we receive this alert, and at what point on the table, depending on how much data usage we want to use before we are alerted.
Just press down on the line and scroll it up or down. This allows us to choose when we receive the alert. We obviously don't want to receive the alert too early because there will be a big gap between the beginning of the limit and the end of the limit.