I use tradingview for my analysis when I'm using a computer and either tabtrader or tradingview Mobile when I'm on mobile.
Firstly, To draw trend lines, check the left side of the chart, you should see a toolbar at the far left corner. The first icon you see is the one to change your cursor.
Skip it and move to the next icon . It's the one that allows you to access drawing tools like horizontal lines (support/resistance) check the list for trend lines. Click it and connect the points to get your points. See:
https://www.babypips.com/learn/forex/trend-lines on how to draw them correctly.
About trend channels, you can draw them manually using trend lines or you can use the parallel channel tool provided by trading view. You can access it the same way you accessed the trend lines tool. See:
https://www.babypips.com/learn/forex/trend-channels for how to draw them correctly.
Here's a snapshot to guide you on how to access both trend lines and trend channel tools on trading view:
Ascending and Descending channels are useful because they can guide you on the appropriate level you should open a position. Ideally, you long at the bottom of the channel or go short at the top of the channel in a downtrend (assuming they don't break). This ensures that you get a nice entry. But like other trading analysis tools, don't rely too much on just trend lines and channels. It's best to combine them with other tools for instance, support and resistance or fibonanci retracement levels.