It appears that you would like to say "I went to the grocery store to buy something today." If so, the most colloquial way to say it in Chinese is to say "今天我去杂货店买(了)东西." Unlike in English, putting the time something was accomplished at the end of the sentence sounds very odd in Chinese. Also, it is not always necessary to add the particle 了to indicate the past tense.

今天我去杂货店买东西了 or 我今天去了杂货店购物。It's strange to say "购物了"。We don't put "今天" on the end. Someone + do + something is the ordinary way.

1. 今天我去杂货店购物了。 2. 我今天去杂货店购物了。 3. 今天我去了杂货店购物。 4. 我今天去了杂货店购物。 1 and 2: Maybe I've been thinking about it for days. 今天我去了杂货店。 O 今天我去杂货店了。 ? 我今天要去图书馆。 O 今天我要去图书馆。 O 我十一点要去图书馆。 O 十一点我要去图书馆。 ？ 我买了东西就走。 O 我买东西了就走。 X 我买东西就走了。 X

今天我们去杂货店买东西了。 我们今天去杂货店买东西了。 一般中文的表达中，喜欢把时间状语放在主语或动词前面。 杂货店在中国人眼中感觉很小，一般只是买点生活用品，所以很少用“购物”来修饰“杂货店”。购物一般用在大型的购物广场，比如：今天我们去武汉展览馆购物了。

我今天去了在杂货店购物 is also right~