GL-MT300N-V2 (mango) Setting up vlans

I have been all over youtube and forums trying to figure out how to configure vlans but none of the information I could find seems to apply to my current setup ):

I have a home 4G huawei router 2/1 provided by my ISP. The router has 3 lan ports and 1 wan port so I figured if I connected it to a Openwrt capable router I should be able to configure vlans. I followed guides online using the GL inet Luci interface so I understand the general concept of setting up switches (and tagging and untagging) and then adding a network interface. But I dont really know how to do it in the practice. Do I have to buy a switch for the router? (I dont need many vlans so if it works with the lan ports I have that would be fine).

While testing I have just had the mango router plugged in trough lan to my 4G router.

I would really appreciate some help and apologise for the basic questions :slight_smile:

You should connect wan port to your 4G router, not lan.

For vlan, I am not sure. The router should have vlan setup but definitely not for that purpose