Verbs in Spanish can be positioned before or after the subject, and you can even omit the subject which will be implied by the verb conjugation. If you have some knowledge of Spanish grammar, you will probably remember that ‘esta’ is a demonstrative adjective, for singular, feminine nouns (this); while ‘está’ is a verb (third person singular of verb ‘estar’: él/ella está – he/she is; and also the second person singular of the same verb, in formal speech: usted está – you are).
Keeping in mind these two previous considerations, it might be easier for you to distinguish these two words, just by the intonation. As a verb, ‘está’ has an accent, while the demonstrative adjective ‘esta’ does not. There is no way to go wrong with that. If the syllable of a word has an accent, you always have to stress the intonation in that syllable. There will be a posting about the rules of accents coming soon :).
To conclude, try to practice saying aloud these sentences in Spanish, and notice the difference of stress in ‘esta’ and ‘está’:
Verb after subject: Esta casa está en venta. (This house is on sale)
Verb before subject: Está en venta esta casa. (It is on sale… this house)
Verb without subject: Está en venta. (It is on sale)
Listen to these sentences in Spanish downloading this file: Esta casa está en venta.mp3