ELI5: How do I best Utilize Gara when it comes to purely using her four unique abilities?

So my Gara finally finished building today and I’m having trouble when it comes to making the most use out of the 2, the ability where she guards herself.

It’s a bit confusing honestly, I tried to understand when to time her abilities correct but it’s just so confusing!

Also, what is the best mode to utilize her 2 and to keep it up forever? That’s what I’m having trouble with.. Does it need to be max rank?

ALSO, I’m still new so I haven’t had the time to fully max out a syndicate to gain access to warframe ability augments but I’m definitely working on it!

But yeah I would really appreciate it.