"This tomato is good."
Translation:Ten pomidor jest dobry.
The pronoun (and adjective) must be agreed with the gender and grammatical case of the noun it relates to. The case used in phrase is ruled by the verb: each verb requires a given case, and there are some verbs that require one of two cases, each case giving a different meaning to the phrase. For example "być" [to be] requires nominative case, or "dać" [to give] requires accusative case.
Ten (pronoun agreed with male, singular, nominative case) pomidor (male gender noun, singular in nominative case) JEST (verb) dobry (adjective agreed with male gender, singular, nominative case). = This tomato is good.
Ta (agreed with female, singular, nominative case) koszula (koszula is female gender noun, singular in nominative case) JEST (verb) ładna (adjective agreed with female gender, singular, nominative case). = This shirt is nice.
DAJ (verb in imperative mood) mi (pronoun) tego (agreed with male, singular, accusative case) dobrego (agreed with male, singular, accusative case) pomidora (male, singular, accusative case). = Give me (the/this/that) good tomato.
DAJ (verb in imperative mood) mi tę (agreed with female, singular, accusative case) ładną (agreed with female, singular, accusative case) koszulę (female, singular, accusative case). = Give me (the/this/that) nice shirt.
Please consult also the table of pronouns in polish with their declension and different genders.
Apparently you use a mobile device and linking is broken on it... Would this work? https://pl.wiktionary.org/wiki/Aneks:J%C4%99zyk_polski_-_zaimki
If "this" describes a noun ten/ta/to etc has to match noun's gender, case and number.
If this is unspecified one thing you use different cases of "to", if these are unspecified things you use variants of te
If this means this one you use ten/ta/to agreeing with gender of a thing you discuss.
"Pomidor" is masculine noun (treated as inanimate noun "m3" or in everyday speech as animate impersonal "m2" http://sgjp.pl/leksemy/#13726/pomidor - the difference is in Accusative singular), therefore if you use an indicative pronoun before "pomidor", the pronoun has to take the masculine form ( http://sgjp.pl/leksemy/#148711/ten ).
- Ten pomidor = This tomato
The word "to" used here does not work as a pronoun, but as a special word that replaces the expression "to jest" ("it is", see https://forum.duolingo.com/comment/26090996 )
- To pomidor = This is a tomato