Linking One To Many

i am new to databases and have developed a ads site

when the user registers they can post ads for free.

i would like to allow one user to post more than one add.

these are my databases

[members]
memberid = autonumber (primary key)
username unique
password
surname
firstname
address
post code
country

[ads]
adid autonumber (primary key)
adtitle
price
picture
contact
date posted
end date

i am guessing i will have to create a one to many database but i am lost at how to do it.

any advice would be appreciated.