Putting output on the chart

A script draws by calling output functions. Each call adds one thing to the chart.

Call	What it does
`plot(series, title, color, linewidth, style, histbase, offset, display)`	Styles: line, stepline, histogram, columns, circles, cross, area, linebr, areabr. `color` can change per bar. `display = display.none` hides it, and `fill` can still use it.
`hline(price, title, color, linestyle, linewidth)`	A horizontal level.
`fill(plot1, plot2, color)`	Shades between two plots, or a plot and an `hline`.
`bgcolor(color)`	Stripes behind the candles.
`barcolor(color)`	Recolours the candle (body, border and wick) on that bar. `na` leaves it alone. When several scripts colour the same bar, the later one wins.
`plotshape(cond, title, style, location, color, text, size)`, `plotchar`	Markers above or below candles.
`plotarrow(series, colorup, colordown)`	An up arrow under the bar where the series is above 0, a down arrow over it where below 0. The arrow size does not scale with the value.
`plotcandle(open, high, low, close, title, color, wickcolor, bordercolor)`, `plotbar(...)`	A candle or OHLC-bar series of the script's own, on the price chart (`overlay = true`) or in its own pane. A bar with any `na` price is skipped.
`indicator(title, shorttitle, overlay)`	`overlay = true` draws on the price chart. Otherwise the script gets a pane of its own.

A script with indicator(overlay = false) and no plot has nothing to put in a pane, so its markers and stripes go on the price chart.

Colouring by condition

//@version=5
indicator("Inside Bar", overlay = true)

inside = high < high[1] and low > low[1]

bgcolor(inside ? color.new(color.yellow, 80) : na)
plotshape(inside, "Inside bar", shape.circle, location.abovebar, color.yellow, size = size.tiny)

Pass na to a colour argument to draw nothing on that bar. color.new(color, 80) makes a colour 80% transparent.

Your own candles

//@version=5
indicator("Heikin Ashi")

haClose = (open + high + low + close) / 4
var haOpen = na
haOpen := na(haOpen[1]) ? (open + close) / 2 : (haOpen[1] + haClose[1]) / 2
haHigh = math.max(high, math.max(haOpen, haClose))
haLow = math.min(low, math.min(haOpen, haClose))

plotcandle(haOpen, haHigh, haLow, haClose, "Heikin Ashi", color = haClose >= haOpen ? color.teal : color.red)