TH sound, is it continuant or stop?

Solution 1:

In standard English, 'th' is always a dental fricative, a non-stopping, continuous movement of air between the tip of the tongue right and the bottom of the top teeth. It is almost exactly the lisp sound.

It is a rare sound in the world's languages, so most language leaners of English have trouble pronouncing it and attempt to approximate it by the fricatives s/z or the stop t/d.

There are some non-standard varieties of English that use t/d naturally instead of the fricative, like for example Sylvester Stallone in Rocky, or any number of street-wise New Yorkers. So don't emulate this unless you want to sound very urban (and a bit out-of-date)

As with most phonetic things, learning it comes with practice and listening and more practice. For 'th' in particular, a little bit of your tongue sticks past the top teeth, so may feel weird (or even rude depending on your culture).