TRIN is one of those indicators that shows a broader perspective on the markets and looks deeper into the underlying market action than what is seen by simply looking at the chart of the S&P or any other index.

Essentially, the TRIN is taken by calculating the following:

(advancing stocks/declining stocks)/(advancing volume/declining volume)

Now this isn't something that you have to calculate by hand. In fact most trading platforms should do this for you. For example on ThinkorSwim it is "$TRIN" and you get it.

So what the TRIN does is allow for you to figure out whether it's the bulls or bears winning the day when trading by determining whether more volume is going into advancing issues, or more volume is going into declining issues (i.e. stocks). When it is the former the TRIN is below "1" when it is the latter the TRIN stays above (by the way the TRIN is sometimes call the "Arms Index" after its founder)

However, the way I was taught was to not look at whether the TRIN is above or below the "1.0" but 1) how it is trending and 2) The level of extremes that it is reporting

First one represents how the day is progressing. If you have a reading of 1.1 - initially you might think that is bearish, but not necessarily if the entire time before it the reading was 1.5, and vice versa when trading below 1.0.

You can definitely do technical analysis intraday in the forms of trend-lines and candle patterns. So that if the TRIN is moving higher with an ideal trend-line and then breaks, there is a good chance that the market is increasingly becoming bullish.

It is also not uncommon to see intraday head and shoulders patterns as well (and inverse ones).

Extremes are important as well because, because you can also see blow-off tops and bottoms. So that if the TRIN gets somewhere around 1.5-1.6 you know there is a very strong possibility of a reversal to the upside in equities, and if you have a move that pushes the index below 0.6-0.5 you may be experiencing a euphoric/blow-off top that eventually experiences some profit taking.

If you have any questions feel free to ask them, and I'd be glad to answer them the best I can.