Ciao Maria Luisa,
"bel, bello, bella, belli,belle" are all adjective meaning "handsome,beautiful,nice".
Depending on the gender of the noun that follows you will need to use:
-bello ( masc. sing) = in front of a masculine noun beginning with s,z (followed by consonant) gn,pn,ps, x
Example : il calcio e' un bello sport (soccer is a nice sport)
-bel (masc. sing.) = in front of a masculine noun beginning with all other consonants
Example: quello e' un bel negozio (that is a nice shop)
-bell' (masc. and fem. sing) = in front of a noun beginning with a vowel
Example: Che bell'uomo! (What a handsome man!)
Che bell'amica che sei = (what a handsome friend you are)
-bella (fem. sing.) = in front of a feminine noun beginning with a consonant
Example: abbiamo passato una bella serata (we spent a nice evening)
-begli/bei (masc. pl.)
begli = in front of a masculine noun beginning with z,s (followed by consonant),gn, pn, ps,x or a vowel
Example: Che begli occhi che hai (what a beautiful eyes you have got)
bei = in front of a plural masculine noun starting with all other consonants
Example: hai comprato dei bei quadri (you bought some nice paintings)
-belle = in front of a plural feminine noun
Example: Lei ha scritto delle belle frasi (she wrote some beautiful sentences)
"bene" can mean "good" or also "well" depending on the meaning of the sentence.
-fare del bene = to do good
-tu parli molto bene l'italiano = you speak Italian very well
"This is a very good course" will be translated in Italian as " Questo e' un buon corso".
I hope this helps.