Most of the smaller submersible pumps don't have any kind of intake fitting on the pumps. the only fitting is on the output side so that you can connect a hose so that you can move the water to another location. The submersible pump is made to just sit in the bottom and suck in water through the intake, which is often covered with a ffilter screen. Some of the bigger pumps actually have an intake port that is threaded for a fitting to connect a hose so that the pump can be used externally rather than submerged. These are made to work either way. But it really depends on what you are wanting to do with the pump. If you are just circulating the solution through all of the totes/buckets that hold plants and connect to the main rez, then I would suggest that you use a standard submersible that is a low gpm. Then connect a small hose that is able to fit inside the pipes/hose that connects the buckets in the system. Place the pump in the last bucket in the series and push the output hose into the connection hose so that the water is pushed into the rez from the last bucket.
However if you are only using this pump to specifically run your solution over to the chiller, then I recommend that you do a separate pump that will pull water from the rez, to the chiller and then feed into the either the rez again or into the first plant bucket/tote so that the coolest water is distributed to the plants while the warmer water is pushed back into the rez.
BTW; don't feel bad or foolish asking about something that you don't know or are not sure about. If you need to know then there is no shame in asking. All of us started out not knowing what we know now. That is why we are here; to share our knowledge and experience with each other so that we all have better, more enjoyable results.