Here are your basic specs to look for when buying a computer for video editing (even older/used models):
Memory/RAM: 8-32 GB RAM or as much as you can afford (ideally at least 16GB)\
Processor: Multi-core Intel i5/i7/i9 models (i9 is best). Preferably 4 or more processor cores.
Storage: At least 256 GB hard drive, 7200 RPM, preferably SSD (fastest), HDD also good... buy as much as you can afford, you can always add external hard drives. Avoid SATA drive if possible.
Graphics card: Depends on video editing software. For example, Premiere Pro and Davinci Resolve do well with both AM-D and N-VIDI-A. (Minimum 2GB memory)
Operating System: Win 10 (64 bit edition)
Nice size screen – -21-28 4K inch minimum
Firewire or Thunderbolt Port built in or as an external dock