Main resources you need to check are
1. CPU
2. RAM - Memory
3. Disk usage
For CPU you can use some commands like top/htop/Atop etc and
For RAM , you can see the current status using free -m and you can see detailed usages from top (then Shift + M).
For Disk usages, you can check them using df -h and then you need to check more using du -sch in the particular partition.
If you can clarify which services or which all resources usages you need to track, then we can help you more accurately with possible exact commands as well