Learn Italian: Non ci sono molti bar qui. - There are not many bars here.

You put non right before ci sono. To make "there is" or "there are" negative in Italian, the word non always goes at the very beginning of the phrase: Non ci sono (There are not).

Why do we use ci sono here instead of just sono?

If you just use sono, it means "they are". To say "there are" (meaning things exist in a particular place), you have to use the full phrase ci sono.

Why doesn't the word bar have a plural ending like other Italian words?

Foreign loanwords that end in a consonant, like bar, computer, or sport, do not change their spelling in the plural. We know it means "bars" here because of the plural verb ci sono and the plural adjective molti.

Why does this sentence use molti instead of molto?

When it means "many" or "a lot of", molto acts like an adjective and must match the noun it describes. Since bar is being used as a masculine plural noun here, molto changes its ending to the masculine plural form, molti.