what is this accrued interest?

hhtt, Thanks. I have some un-invested cash in retirement account. Interest rate is very low 0.15%. so I tried to buy 1k treas t bills. It showed 2/15 maturity, but it charged me 1009 since 9 is accrued interest. I am so confused since some article said it will only return face value of 1k. why e trade charge 1009? what is this accrued interest?

I want to learn more how to buy brokered cd and tbill in retirement account since there are some un-invested cash and stock is high now.