Hello,
eth0 denotes a physical switch device within the router, which appends ports LAN1, LAN2 and LAN3.
eth1 is a separate hardware device notation for WAN port.
eth0.1 usually means VLAN with ID 1, which is default VLAN. This is a logical notation, thus not necessarily associated with a physical port, but rather a tag value in the packet's header.
br-lan is a bridged interface, which, depending on your router's configuration, means that it can contain several physical interfaces (eth0, wlan0(wireless LAN interface)) under a single virtual interface.
Best regards,