Hello, I don't have much experience with microcontrollers, etc but I have done a bit of research already and haven't found anything useful. Essentially I am trying to connect a USB flash drive to an Arduino microcontroller to check if a file is in the USB. I'm not sure if this is possible though. Do I need external products to make this possible? Do I need a specific Arduino model to make this work? I have never used an Arduino before. Thanks for your help! 
You need to look for devices with USB Host support, for instance the Arduino Due.
There is a library called USBHost. Reference here:
However, the library only includes examples for connecting a mouse or keyboard. I am not sure how much work is required to use the library for mass storage classes.
May I ask why you want to use USB flash drives? If you are looking for large memory, there is much better support for SD cards because you can connect using a simple SPI peripheral.
Consider that a Pi Zero would be better provisioned to perform this job, for similar or better price and size.
Klaus_K:
May I ask why you want to use USB flash drives? If you are looking for large memory, there is much better support for SD cards because you can connect using a simple SPI peripheral.
Thanks for the reply. I am wanting to make a device that moves a motor if a USB flash drive has a certain file in it. it will be a text file and won't be massive and will be reading the file only. The only data I need to be stored on the Arduino is the code to know what file it is looking for.
How about using a micro SD card instead? That USB drive could indeed be the kind that takes a micro SD card (also known as a micro SD adapter), which any regular Arduino can readily deal with. Adapters like this one are cheap and easy to come by:
woahcool:
I am wanting to make a device that moves a motor if a USB flash drive has a certain file in it. it will be a text file and won't be massive and will be reading the file only.
I would seriously reconsider and use a SD card. This will reduce the requirements on the Arduino board and the modules like the one wvmarle showed are cheap and easy to use.
The Pi Zero Paul__B recommended can handle USB host, mass storage and file system functions because it runs Linux but would be a total overkill for what you want to do. As a plus you could implement this function in all programming languages known to mankind.
woahcool:
I am wanting to make a device that moves a motor if a USB flash drive has a certain file in it. it will be a text file and won't be massive and will be reading the file only. The only data I need to be stored on the Arduino is the code to know what file it is looking for.
Still very much the "XY Problem". 
While a USB flash drive is a very negotiable item nowadays (but there are substantial risks picking up an "orphan" one dropped on the street and "trying it out"), there are probably more practical versions of a digital "passkey" such as the Maxim "iButton".
These interface directly with an Arduino (or ESP) such as a Nano, no USB interface required. While you cannot load a whole text file, a second Arduino can of course connect to a PC via USB to manage the key information and you can have "master" keys which transfer updates and the like.
Klaus_K:
The Pi Zero Paul__B recommended can handle USB host, mass storage and file system functions because it runs Linux but would be a total overkill for what you want to do.
Overkill perhaps, but compact, easily programmed and quite inexpensive really, entirely competitive with the other options. 
Paul__B:
Still very much the "XY Problem".While a USB flash drive is a very negotiable item nowadays (but there are substantial risks picking up an "orphan" one dropped on the street and "trying it out"), there are probably more practical versions of a digital "passkey" such as the Maxim "iButton".
...
These interface directly with an Arduino (or ESP) such as a Nano, no USB interface required.
Thanks for the reply. I know I'm not giving much info on it, which is mainly because I don't want to put my idea on the internet right now as it's actually a part of a product I am working on which I don't want others to catch onto right now. I won't be using anything like RFID or anything without an interface. I am intending to redesign the interface of the USB/micro SD card to suit the dimensions/interface of the product. This is why I thought going with a USB flash drive would be suitable as it appears that it would be harder to configure the interface of a Micro SD than it would a USB, but if it is smarter to go with the micro I will give it a shot. I am very proficient in Python, do you know if there is a way I can use my knowledge in python with an Arduino? Or will I have to learn the Aurdino language for the project? Thanks
If you know how to program and you know a bunch of languages already, learning another programming language becomes just learning another programming language. You don't have to relearn programming itself.
The Arduino is programmed in C++.