I am just beginning to learn.
The issue I run into is that I learned that identifying the declension of a noun means I need to know the genitive. Well…if all I have is the noun as it is written, how do I do that? Perhaps all I have is obviously an ablative. (ibus for example)
Most of the time, when I enter the word I am reading into a dictionary, just get back “not found”. Yeah, because I cannot figure out what the base noun is. Is there a way to figure out the base noun from any word?
when I enter the word I am reading into a dictionary
I think this might be the step that's getting you. I would first and foremost recommend a paper dictionary, but if that's not possible, I'd recommend an online dictionary you can "scroll" through.
Take for example Lewis' An Elementary Latin Dictionary. Here you'll see the whole dictionary divided first by initial letter, than in groups of words, then finally individual words. If you're unsure of the nominative of a word, getting as close as possible to the root means you'll either eventually stumble upon the word or a related word that provides you that base word. It's easier to do this with a paper dictionary, so that's why I suggested it as my first choice.
Where things can get tricky is if the oblique form and the nominative are very different, you'll sometimes have to spend an inordinate amount of time looking. Like, say, you have agris, and you don't know the nominative. In cases like these, one online tool is a morphological parser, such as the one by Perseus. You type in the word, and it gives you all possibilities of what that word could be.
Of course, after a while, as you learn words, you'll just remember them. And there are patterns of inflection. So learning your case endings and several hints as to what, e.g., the third declension does in oblique cases will help you recognize the words on sight.
Let me strongly recommend en.wiktionary.org, which, despite it's many shortcomings and downright errors, will do exactly what you want.
For instance, say you want to find the noun declension and meaning for hominibus. Go to the English Wiktionary, and enter hominibus. Hit return and it will take you to this page, which will tell you that hominibus is the ablative or dative plural of homō. Clicking on homō will bring you to its dictionary entry and give you a cursory definition, and, if you scroll down, a table of declensions, which will tell you that it is a thrid declension noun with a genitive of hominis. Actually, it will give you all the declensions (whether attested or not, but in the case of homo they are all attested) along with a very cursory definition which might give you a hint to its meaning.
If you want a full definition along with how it is used in literature, you will need to go to Perseus, as Cmw pointed out in his excellent answer.
The simple answer is, No, there is not. Just as there is no reliable way to work out the base form of an English verb from the past.
You are used to thought <- think, and grew <- grow (and the fact that we don't generalize these to drink -> *drought or glow -> *glew) but to a learner, this is just something that has to be learnt.
In both cases, there are patterns which often help. If a Latin noun ends in -i it's probably a genitive singular or nominative plural of a second declension noun (nom. sing. in -us or -um; but if it's -ri, then the nom. sg. might be -er). But it might be a dative singular of a third declension noun, in which case the nom. sing. is possibly in -is, but might be different, and even have a altered stem.
Going the other way, a noun in -us most often forms its gen.sing. in -i (2nd declension); but it might be in -us (long 'u' - haven't readily got a macron - 4th declension); and there are odd cases like corpus, gen. sg. corporis (3rd declension).
As I say, there are some patterns, but in the end it requires some learning.
