Many Classical and Steel String Acoustic Guitars only come with one strap button on the bottom of the guitar's body.
Normally you would use a guitar strap that comes with a string to tie around the headstock of the guitar, this provides a more balanced feel for larger-bodied acoustic or classical guitars.
PLEASE NOTE: Martin guitars do not come with the bottom strap button fitted - It is usually shipped separately within the guitar case to avoid damage during transit and requires inserting into the pre-drilled hole once you receive the guitar.