The world of IDS/IPS software is fairly complicated and, in order to get real benefit from any of them (not just feeling good about having some software installed), you often need a high level of knowledge of the domain and time to configure, watch, maintain, and customize your IDS software.
That said, some of the best IDS/IPS software out there is Bro and Snort. Bro is better but requires more expertise. Snort is a simpler and more popular. With most IDSes, you can configure them as IPSes in response to events.
Dialing things back to much simpler and a much better starting point if you don’t have any firewall yet, services like HeatShield will help you configure a network firewall without needing to do anything from the command line. If you prefer the command line, each Linux distribution has different iptables frontends that their users prefer (for example, ufw on Ubuntu).
The right choice (and combination of choices) depends a lot on how much time and expertise you have.