What is the best way to kill weeds and crab gr I think I've tried back

Were are the weeds?

Pre-emergent weed killer/fertilizer in the spring before weeds/crab grass really get a foothold is probably your best strategy, Laura.

Once you have it, then proper lawn care practices to encourage a dense stand of vigorous grass are the best way to handle them. For example, mowing height can have a big impact. Lawns mowed higher (over 2½ inches) tend to have less problems with annual grasses such as crabgrass.

See if you don't find this informative:

https://www.agry.purdue.edu/turfnew/pubs/AY-10.pdf

Sorry I should have said not in the grass but actually in flower beds. I did the tarp first etc. But it rips through that and still keep coming back

Tar paper before planting

Great thank you