How to interpret browser wait time in browser snapshot

Question

I am doing website performance monitoring and optimization.
When you look at navigation timing API there are many wait time between diffrent segment of a single page request.

Image:https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/NavigationTiming/timing-overview.png

The below metrics we are getting navigation timing API.

{
navigationStart,
unloadEventStart,
unloadEventEnd,
redirectStart,
redirectEnd,
fetchStart,
domainLookupStart,
domainLookupEnd,
connectStart,
connectEnd,
secureConnectionStart,
requestStart,
responseStart,
responseEnd,
domLoading,
domInteractive,
domContentLoadedEventStart,
domContentLoadedEventEnd,
domComplete,
loadEventStart,
loadEventEnd
}

On computing the metrics we get the wait time on each segments.In that

Wait time before Redirection - diff(navigationStart, redirectStart)
Wait time after Redirection - diff(redirectEnd, fetchStart)
Wait time before DNS - diff(fetchStart, domainLookupStart)
Wait time before TCP - diff(domainLookupEnd, connectStart)
Wait time after TCP - diff(connectEnd, requestStart)
Wait time after Response - diff(responseEnd, domLoading)


Can anyone explain what work done by browser during each wait time of above mentioned.
What are all the significant factors influenced to increase and decrease in wait time.

Refrence: https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/NavigationTiming/Overview.html#process