What do I need to be able to use my 2015 Air 13in on a external monitor ?

[DBZmusicboy01]

Like a 1080 Dell monitor.
I have a HDMI cable but the Air doesn't have a port for it. I also want to use my 4K TV in the future as well.

 

[thats all folks]

the thunderbolt port on the Air also carries a Display Port signal. you can get an adapter or cable that goes from Mini Display Port to DVI, HDMI or full size Display Port. That port supports up to UHD, 3840 by 2160.

 

[DBZmusicboy01]

the thunderbolt port on the Air also carries a Display Port signal. you can get an adapter or cable that goes from Mini Display Port to DVI, HDMI or full size Display Port. That port supports up to UHD, 3840 by 2160.

The mini display port to HDMI also supports 4K output ?

 

[thats all folks]

depends on the adapter. for example this one,
http://www.bhphotovideo.com/c/product/1181527-REG/macally_mdhdmi4k_mini_displayport_to_hdmi.html
says it does.