Please forgive me if I've done a similar post in the past, but the way I think to explain how I view things tends to change from day to day, so this will probably still be a little different lol.
First, I want to briefly explain how I view the Gods and Goddesses out there. If you ever watched HollyDaisyRose's YouTube channel (Sam now has a new channel, but I forgot what it is...Witchontherocks, maybe?), my beliefs are similar to hers. I believe that the divine spring from one source, THE Source, a supreme God, the energy of the Universe... Whatever you want to call that.
I believe that they were created by humans calling on certain aspects and naming those aspects (Aphrodite, Isis, Ishtar, Hekate, Hades, Zeus, Pan, etc.) of The Source. I believe that because of human emotions and needs and all those things, these aspects of The Source were given faces, names, histories, etc. and eventually, because of humans believing in them so strongly, sort of came into being. Basically, humans created them, is what I believe. You know how hypochondriacs think they're sick so strongly that they become sick? Or how some people are convinced so thoroughly that they're being haunted that they manifest a poltergeist or whatever you want to call it? I think that individual deities came into being in a similar way.
Now, I'm not saying that they are NOT real, because I believe they are. I'm just saying that I think they are facets of The Source, but not separate from It. I believe they can take a form in visions or something and reveal themselves to humans in a way that is most appropriate for each individual, so everyone will see each aspect of Deity/Divinity/The Source differently, but they will be similar because of the aspects they represent. I hope that makes sense...
Now, as far as invoking Deities is concerned, you probably realize by now that I don't do things the way many books suggest. I've tried it, it didn't work for me. I personally just find that praying/talking/calling out to the particular Deity you're asking assistance from is sufficient, at least for me. I don't do anything elaborate, I simply meditate and clear my head of everything else and focus solely on the Deity I need, letting an image form in my mind, or hearing them respond, whatever comes naturally. I tend to "fly by the seat of my pants" during rituals and the like. I think that the energy from The Source is present everywhere, including within each of us, and that once you have realized that, felt a connection, etc., it's easier to connect with The Source through a certain aspect, without much or any formality.
When first starting out, I do think that the formality of going through planning and executing a ritual (or 50 haha) or spell, etc. can be beneficial. It helps keep you focused on the task at hand and helps to break down any barriers that your conscious might have up that would prevent you from achieving your goal for the occasion. If that's what feels right for you, then by all means continue! I do believe that it's equally helpful to try different things, though. Even if you don't actually adopt a certain practice, sometimes it might spark your creativity and give you an idea to try.