What is the difference between ps and top command?

top is mostly used interactively (try reading man page or pressing "h" while top is running) and ps is designed for non-interactive use (scripts, extracting some information with shell pipelines etc.)

top allows you display of process statistics continuously until stopped vs. ps which gives you a single snapshot.

Another point:

ps - Reading Process(ps) Information
top - Resource Monitoring like top resources using cpu, memory usage and more.