OAT stands for Obligations Assimilables du Trésor — fungible treasury bonds issued by the Algerian government. They're priced in percentage of par (face value) rather than in DZD, because a bond's face value is fixed and what varies is the discount the market applies to it.
An OAT trading at 98.5% with a 4% coupon and three years to maturity means: pay 98.5 DZD today per 100 DZD of face value, receive 4 DZD per year in coupons, get 100 DZD back at maturity. The yield to maturity is the discount rate that makes those cash flows equal the price.
The Treasury tab on /market opens with the yield curve — the visualisation of yields across maturities. Steep curves mean the market expects rates to rise; flat curves mean expectations of stability.