Faq
It's somewhat complicated. As every input device requires some time to start-up, playing them directly in CasparCG is not best idea. In fact, only Decklink inputs have the time small enough to be acceptable in some circumstances (it's less than 0.5 second). In this case, enter DECKLINK 1 as live device name, assuming your input card is the first in order:
Actual streaming video have to be decoded and provided to Decklink input with other means, i.e. using second Decklink card and OBS Studio, or bare FFMpeg (compiled with --enable-decklink).
Other (better) option is to use route producer in CasparCG. In this case the input will be played permanently on another CasparCG channel (you'll have to setup it in casparcg.config), and routed when required to main CasparCG channel using route://2 as input name (assuming the additional channel is 2nd channel in casparcg.config). This also removes necessity of using two separate Decklinks only to route the signal to CasparCG input.
It wold be useful to add some output (NDI would be cheapest) to the input channel to see actual stream before it's aired.
Using TVP's fork, both kinds of inputs (NDI or DECKLINK) can be initialized for a channel from casparcg.config. Yo can know more about this from release notes(6.1a). It's also documented in commentary section of casparcg.config file.