Big companies have a high demand for drivers due to turn over rates in the industry and them not offering a better deal than the smaller companies, so it's not unusual to get conditional job offers while still in school or hell some companies run their own schools and will give you a conditional job offer as a part of applying to that school.

All this means is that if you sign it and you get your CDL, you then have to attempt to complete/pass the points they listed (which are just a fancy way of saying normal job stuff plus a drug test and license check). Upon the successful completion of those you'll then be fully hired into Swift and receive a bit of compensation for the time.

If you don't sign it nothing will happen, if you do sign it but don't get your CDL nothing will happen, and if you do sign it and do get your CDL swift will expect you to follow through but afaik you or they can terminate the agreement for any reason unless someone is is making you sign it as part of an offer to cover tuition then it usually comes with a lot more legal baggage since money is now involved. I don't recommend signing multiple, just one.

As far as if you should sign with swift, you could wait for other offers but as far as carriers that are willing to hire a newbie with no experience goes swift isn't the worst option. Pay will be a bit shit but that's true of any mega, company is gonna be a bit of a mess but that's also true of any mega, but they also look the other way for all the minor fuck ups a newbie makes which can be a good and a bad thing. Good that you'll just get a slap on wrist at most but bad in that as long as you aren't the worst driver they don't really try to help you improve which can lead to bad habits.