I am not able to kill these weeds in my garden.
Click on any image for full size
Gardening & Landscaping Stack Exchange is a question and answer site for gardeners and landscapers. It only takes a minute to sign up.Sign up to join this community
It looks like you have clover and thyme and grass all co existing in the same area. This mix is actually recommended for a low maintenance area.
I do not recommend Round up to solve this. You would have to apply it over the whole area and really soak it in then you would not be able to do replanting for at least a week or more.
It is just as effective to dig up the area with a turf spade and re sod. You would be doing that anyway if you apply Roundup. Or, if you wait till fall you can over seed with grass.
If that is thyme in the photos then the question is how can it compete with grass? Normally grass has no problems out growing it. Thyme thrives on dry soils with lots of sun. Consider applying compost or other organic matter to help retain moisture. This will prevent the thyme from reappearing from any seeds.