Let's try to solve your problem with me :-),
So you have a layer (table) with the name "city", which are represented as points with the name "points" with the type of geometry (Point, 2154) and a column with the name "pop" with the type of integer in which we store population data. If this is the case, let's move on, namely run the script:
create table city_pop as
SELECT id, ST_Buffer (points, pop*0.01) geom_byffer, pop
FROM city ORDER BY id;
As a result of the execution of the script we will get a new table with the name "city_pop", with the columns "id", "geom_byffer", "pop" where we have transferred the data from the source table and created buffer zones like Polygon with a ratio of 0.01.
Remember that in the new table you can leave the names of the columns as in the old table, or you can rename them at your discretion. You have to adjust the proportionality coefficient so that when you visualize your buffer zones you will be able to see them clearly.
Well, here we are all at the goal, believe in yourself, learn and further and do not be afraid of falling,
success to you...