It looks like you are evaluating ESXi 7.0 which consumes up to ~130GB on the installation disk by default.
For lab/evaluation purposes you can reduce that, by limiting the OSDATA partition size by appending e.g. autoPartitionOSDataSize=24576 to the boot option while installing ESXi 7.0.
The ESXi installer creates a default datastore with the rest of the space from the disk which you have ESXi installed on (It depends on if you use a SD/USB or other kind of media). If you use ESXi 7.0 than there is a new partition layout and ESXi claims up to 120GB as a OSDATA disk, a few GBs for the boot banks and the rest is used for the default datastore.
If your Dell server have a RAID controller you need to create a RAID0 for our additional disk. After that "vDisk" is created on PERC level you have to create a new Datastore by pressing the "New Datastore button. You have to follow the wizzard to create a 1TB VMFS 6.0 filesystem.