I work in sales and I mainly deal with manufacturers and retailers.
I work in the sales department and most of my work involves dealing with manufacturers and retailers.
I work in sales and I spend most of my time dealing with manufacturers and retail businesses.
「わたしは営業です。主に製造業、小売業を担当しています」＝ I work in sales and I mainly deal with manufacturers and retailers. / I work in the sales department and most of my work involves dealing with manufacturers and retailers. / I work in sales and I spend most of my time dealing with manufacturers and retail businesses.
ボキャブラリー
製造業 ＝ manufacturers
小売業 ＝ retailers / retail businesses
担当する ＝ deal with / be in charge of
主に ＝ mainly / most of the time
わたしは営業です ＝ I work in sales / I work in the sales department / I'm a salesman (salesperson)
イギリス 
