Pronunciations of と/ど, た/だ, ち/じ


I am a Japanese beginner, and a lot of times I find it hard to distinguish the
pronunciations betweenた/だ, と/ど, ちじ etc. For example, わたし, the pre-record
pronunciation online sounds like “wadashi” to me; 友達 (ともだち）sounds like
“domodaji”. For the first example, I asked a Japanese friend, he told me
“watashi” and “wadashi” sound the same to Japanese native speakers, ie. both
pronunciations are acceptable. It’s not I don’t believe my friend, but just
want to double check whether it is like what he told me in reality. If there
is no distinction between the pronunciations of “ta”, “da” “to”, “do” etc.,
what’s the meaning to have different alphabet た, だ, と, ど?

Thanks so much

