Monitoring Daily Data Usage on Linux

edit: I am using MX Linux xfce and I am open to installing other packages, I ain't married to any of these packages.

https://imgur.com/a/SAHnCV0

I have installed `vnstat` package and it's quite handy. I have a few questions about it though.
1. What is `rx` & `tx` mean in this package?
`rx` stands for `received`
`tx` stands for `transmission`

Is there a command to check data usage on my system using this? I mean, I want to create a Add an item to my panel which will show me my daily data usage updating it every minute. Basically, I want to to see what the arrow points to **on the panel next to my date** and I want it to update it every minute. I have 1.5GBs of data a day and I usually am not able to use it efficiently or I use too early and spent hours without data. So, I want to try and handle this problem by monitoring my data.

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Note: I want to measure gauge data speed here, not do a speed test on how fast my internet is.

Also, I want to monitor the instantaneous rate of data usage and for that package `bwm-ng` does a great job, but I want to see in the panel and I want it to update every `0.5 s` how can I achieve this?

I would like for a command to either view `red arrow` or the `black arrow` with the right mark depending upon which of them is `instantaneous data speed`

https://imgur.com/a/cItDaEg

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Note to Future self:
`rx` : `received`
`tx` : `transmission`
`lo` : `local loopback`
`wlan0` : `ethernet`