user36266: I am a newbie in animation and I am learning by watching different projects.
And I found this expression, but I try to find information and I am not lucky.
comp("Render Comp FHD").layer("Controls").effect("Bg Color")("ADBE Color Control-0001")

this expression is used to set the background color
Please I would like you to explain or give me links to deepen the subject

user1950: That comp links to a layer in a comp called "Render Comp FHD" that has an effect called "Bg Color", which is most likely an expression colour control effect (found in effects>expression controls, they do nothing, but can be used in expressions).
You can create an expression like this by pick-whipping to the effect in question. If it's in another comp you can open the effect controls window (shiftctl/⌘t) for the layer you want to be the controller, and click the padlock on the window tab. That will keep it open when you switch to the other comp, and you can drag the pick-whip to it.
Expressions reference here: https://ae-expressions.docsforadobe.dev/

36266: <p>I am a newbie in animation and I am learning by watching different projects.</p>
<p>And I found this expression, but I try to find information and I am not lucky.</p>
<pre><code>comp(&quot;Render Comp FHD&quot;).layer(&quot;Controls&quot;).effect(&quot;Bg Color&quot;)(&quot;ADBE Color Control-0001&quot;)
</code></pre>
<p>this expression is used to set the background color</p>
<p>Please I would like you to explain or give me links to deepen the subject</p>
 1950: <p>That comp links to a layer in a comp called &quot;Render Comp FHD&quot; that has an effect called &quot;Bg Color&quot;, which is most likely an expression colour control effect (found in <strong>effects&gt;expression controls</strong>, they do nothing, but can be used in expressions).</p>
<p>You can create an expression like this by <a href="https://helpx.adobe.com/after-effects/how-to/link-properties.html" rel="nofollow noreferrer">pick-whipping</a> to the effect in question. If it's in another comp you can open the effect controls window (<kbd>shift</kbd><kbd>ctl/⌘</kbd><kbd>t</kbd>) for the layer you want to be the controller, and click the padlock on the window tab. That will keep it open when you switch to the other comp, and you can drag the pick-whip to it.</p>
<p>Expressions reference here: <a href="https://ae-expressions.docsforadobe.dev/" rel="nofollow noreferrer">https://ae-expressions.docsforadobe.dev/</a></p>
