where do you add the hydraulic oil? Do I have to raise the cab?
See this attachment. I had to guess which model of 262C you have but I think it will work. It sounds like you could really use an Operation/Maintenance manual. Post a Serial Number to help identify the correct manual for your particular machine. They cost around $50 and can be very helpful in situations like this.
You don't technically have to raise the cab, but if you are putting anything more than a quart or two you pretty much have to. Raise the cab and put the boom all the way up and set the boom lock down. Note that the reservoir level will be artificially low with the boom all the way up. Clean the reservoir cap off before you open it. It likes to collect a lot of dirt where it is.