Either and neither can be used to agree with negative statements. 'I don't like horror films!' I don't either/ neither do I. ( you can also say 'me neither' but this is very informal English) Too can be used to agree with positive statements. I love pizza! I do too/ me too ( you can also use 'so'. 'So do I' We also use 'either... or' to say one or the othe. 'Either Peter or Mary will help you.' and 'neither...nor' to say 'not one and not the other 'Neither Peter nor Mary will help you'.

"either" is used in negatives I like coffee too. I don't like coffee, either. That's the only difference and it is simple! "neither" is another word and is used in a completely different construction. Look it up and you can learn.