It depends on what you mean by computer... I think the very first was the VIC20, followed immediately (six months) by the Commodore 64 with a 1541 floppy drive and modified firmware (it ran four times faster than the original).
I used it to create and sell the first (small) warehouse management programs.
It was 1981/1982, and the Commodore 64 arrived directly from America thanks to an American friend (it cost me an arm and a leg). Fortunately, the following year they began distributing it in Europe at a more affordable price.
In 1983, I assembled a PC XT as a school exercise... thanks to Peter Norton and his manuals. I used it to create the first "booth" for ATMs in my city, where the free/busy signal and door opening were managed by the modified XT firmware via the parallel port.
What wonderful days.
.... Uhmmm really the first computer used was at school (1980), a machine with CP/M but I don't remember the hardware system. I Know it was connected to a Unix datacenter.