Can someone please breakdown the formula below into bite-sized chunks or explain it to me

[SethDark]

=IF(ISERROR(SUMIFS(INDIRECT("'"&AV$4&"'!"&"$A$49:$EO$49"),INDIRECT("'"&AV$4&"'!"&"$A$4:$EO$4"),AV$5,INDIRECT("'"&AV$4&"'!"&"$A$5:$EO$5"),$A53)),0,SUMIFS(INDIRECT("'"&AV$4&"'!"&"$A$49:$EO$49"),INDIRECT("'"&AV$4&"'!"&"$A$4:$EO$4"),AV$5,INDIRECT("'"&AV$4&"'!"&"$A$5:$EO$5"),$A53))+IF(ISERROR(SUMIF(INDIRECT("'"&AV$6&" "&$A$48&"'!"&"H:H"),$A53,(INDIRECT("'"&AV$6&" "&$A$48&"'!"&"J:J")))),0,SUMIF(INDIRECT("'"&AV$6&" "&$A$48&"'!"&"H:H"),$A53,(INDIRECT("'"&AV$6&" "&$A$48&"'!"&"J:J"))))+IF(ISERROR(SUMIFS(INDIRECT("'"&AV$4&"'!"&"$A$48:$EO$48"),INDIRECT("'"&AV$4&"'!"&"$A$4:$EO$4"),AV$5,INDIRECT("'"&AV$4&"'!"&"$A$5:$EO$5"),$A53)),0,SUMIFS(INDIRECT("'"&AV$4&"'!"&"$A$48:$EO$48"),INDIRECT("'"&AV$4&"'!"&"$A$4:$EO$4"),AV$5,INDIRECT("'"&AV$4&"'!"&"$A$5:$EO$5"),$A53))+IF(ISERROR(SUMIF('Manual'!$A$6:$A$81,$A53,INDEX('Manual'!$B$6:$KO$83,0,MATCH(AV$5&" "&AV$4,'Manual'!$B$5:$KO$5,0)))),0,SUMIF('Manual'!$A$6:$A$81,$A53,INDEX('Manual'!$B$6:$KO$83,0,MATCH(AV$5&" "&AV$4,'Manual'!$B$5:$KO$5,0))))

[FDibbins]

Hi, welcome to the forum

Hard to say without seeing what it relates to, but it looks to me like the following...
Basically, it is summing 4 different sets of data, based on a sheet name provided in column AV, and then adding those totals together.

The whole thing could be shortened to this...
=IFERROR(
SUMIFS(INDIRECT("'"&AV$4&"'!"&"$A$49:$EO$49"),INDIRECT("'"&AV$4&"'!"&"$A$4:$EO$4"),AV$5,INDIRECT("'"&AV$4&"'!"&"$A$5:$EO$5"),$A53),0)
+IFERROR(
SUMIF(INDIRECT("'"&AV$6&" "&$A$48&"'!"&"H:H"),$A53,(INDIRECT("'"&AV$6&" "&$A$48&"'!"&"J:J"))),0)
+IFERROR(
SUMIFS(INDIRECT("'"&AV$4&"'!"&"$A$48:$EO$48"),INDIRECT("'"&AV$4&"'!"&"$A$4:$EO$4"),AV$5,INDIRECT("'"&AV$4&"'!"&"$A$5:$EO$5"),$A53),0)
+IFERROR(
SUMIF(Manual!$A$6:$A$81,$A53,INDEX(Manual!$B$6:$KO$83,0,MATCH(AV$5&" "&AV$4,Manual!$B$5:$KO$5,0))),0)

AV4 would contain a sheet name. This is being used by the SUMIFS, via INDIRECT, to determine which sheet to use for the sum
So, if AV4 contained "Sheet1", that formula would reduce to...
SUMIFS(sheet1!$A$49:$EO$49,sheet1!$A$4:$EO$4,AV$5,sheet1!$A$5:$EO$5,$A53),0)...
etc

[STUARTXL]

This is difficult since the formula is referencing a sheet that we do not have access to.

However, Excel allows you to see how a big formula like this is condensed further and further (your 'bite-sized chunks'), until the result is generated. It does this through the 'Evaluate Formula' function. Navigate to Formulas > Formula Auditing section > Evaluate Formula and each time you click 'Evaluate', Excel will shorten the formula a bit more for you, until it has been completely solved.

Note that this function only shortens one part of the formula at a time to make it easy for you to understand what is going on. These are underlined to allow you to watch what happens.