It depends and there are a LOT of options here, partly depending on what you want to do with it, mostly depending on where the "original" source of data is, if anywhere.
If there is no original source of data, I'd probably recommend using a CSV file (you can build one in Excel or Google Sheets). If you save it as a lookup you can use that to enrich other data. That should be outlined fairly well in the following docs (and places those docs lead - keep reading and following links!), but if you get 80% of the way through and can't figure out the rest, you'll probably want to create a new question specifically about the problem you are running into.)
https://docs.splunk.com/Documentation/Splunk/8.0.6/Knowledge/Aboutlookupsandfieldactions
Likewise, if there is a spreadsheet of it already, maybe just save that as a csv file (the right tab of it, of course) and use that as above. Someone will need to update that every now and then.
If this data is already somewhere in a DB or app, you might be able to pull it into Splunk directly. If a DB, you may be able to use DB Connect. If some other app, hunt around in Splunkbase to see if you can find an app that pulls the data in. This has the benefit (probably) of being able to be updated regularly without needing someone to export data.
You may be asking an *entirely* different question, though! If you are instead asking "How do I make a pretty chart or graph of who has which device, if I have apache web logs?" (Substitute whatever log source you have!). Then the answer gets even more complex, but also maybe easier. Different anyway. 🙂
There, I'd suggest doing the following -
1) Take the Free Splunk Training course "Fundamentals 1". It's self paced and takes, oh, maybe half a day to a day (going from what others tell me, your time may differ).
https://www.splunk.com/en_us/training/free-courses/splunk-fundamentals-1.html
2) Then find and download the Splunk Tutorial data and follow it.
https://docs.splunk.com/Documentation/Splunk/8.0.6/SearchTutorial/WelcometotheSearchTutorial
Happy Splunking!
-Rich
