what's 'to' and 'for' mean?

[Lela]

English Grammar Tests, Elementary Level

ESL/EFL Test #106 "Beginner Grammar Questions Test (1)", question 7

I was out when you called. I went to the store ......... buy some milk.

(a) for
(b) to
(c) order to

English Grammar Tests, Elementary Level

ESL/EFL Test #106 "Beginner Grammar Questions Test (1)", answer 7

I was out when you called. I went to the store to buy some milk.

Correct answer: (b) to
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i don`t understand `to` and for, what `s mean?

Lela

[Mister Micawber]

.
Both prepositions have many, many meanings, Lela-- too many to list here.

In this sentence, however, only 'to' fits the grammatical structure. Here, 'to' = 'in order to' = 'for the purpose of (buying)'. 'For' can also mean 'for the purpose of' getting something, but would be followed by the noun: 'I went to the store for milk'.
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Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber