If I'm understanding your question correctly, you want to sum the values of the column. The formula you have (which, I'm a little confused by, because the field name of the SUM function doesn't exist in your screenshot) will sum the values of the specific cell.
In order to get the sum of values from a field, the easiest way is by looking at the field summaries (e.g. along the group header for "Strategy Development", it displays sums for a few numerical/formula fields). There are a few ways to do this: with a group, with a view, or with a field.
With a group: You've already done this for "Strategy Development" – all you have to do is group by "Technology", and each group header will have the sum (or other calculation you choose, e.g. max, min, avg) for applicable fields, no additional formula required. This is the most straightforward solution.
With a view: Create a view with the filter "Technology" = Social Media. You'll see the sums in the field footer (unless you group records, in which case they'll show in the group headers). The weakness of this approach is that you'll have to create a separate view for each case you want sums for.
With a field: Create a field with the formula:
IF({Technology}="Social Media", {Weighted Results})(the IF function in Airtable doesn't require the "else" argument"), then look at the group header or field footer for the sum. The weakness to this approach is that you'll have to create a separate field for each criteria you want to filter by, but the benefit is that you'll be able to see the result in any view.
However, if you're hoping to get the value for use in another table, or for copy and paste... it's a bit more involved. For copy and paste, you'll want to use the pivot table extension: https://support.airtable.com/docs/pivot-table-extension
For another table, you'll want to link all the records to that second table (you don't have to be selective here, since the rollup field has the ability to filter records), and then do a rollup: https://support.airtable.com/docs/rollup-field-overview
