The oil you need to lube a treadmill is silicone based. These are sold at *Amazon for a reasonable price of only $13 at the time of writing. This is the one to go for if your manufacturer doesn't recommend any specific oil themselves. If they do then always buy what they recommend. This way if anything goes wrong with the treadmill then the engineer can't blame it on the lubricant.
Sometimes the manufacturer will make their own lube for you to use and in this case it's obvious to buy and use that. Lubricating the belt is easy and involves loosening the belt first of all. This involves a screwdriver and you loosen the screws at the end of the belt or deck and this loosens the belt. You then apply the lube width way all along the belt.
When you've applied the lube, allow the machine to run by itself for say 5 minutes at 5 mph. This ensures the lube is spread everywhere along the belt and where the motor touches the belt so it lubricates that bit. You can use the lube on any parts of the motor or treadmill that are squeaking or making a noise and this should help prevent or reduce that.
It's really important that you regularly maintain your treadmill as doing so can make the treadmill last anything from 7 to 12 years. You can pay someone else to maintain the treadmill for you but that will cost a lot in that the initial call out will cost the most. But paying someone is something you may want to do if you can afford.
Lubricating the belt will take around 5 to 10 minutes and there are plenty of videos of it on youtube to help guide you as to what to do. I think it's easier watching a video of someone else doing it than explaining it in writing. Nearly all treadmills work the same way where lubricating goes you won't find any variation. Remember though to just stick to special treadmill lube to do the job and you can't go wrong.