Max 8 reverse effect ?

I'm new to Max, I don't understand how to use grove and buffer objects...!

ah, i understand, no worries then... in that case, i should point you first to the tutorials and docs:
https://docs.cycling74.com/max8
but if you want to get straight into sampling, no prob, just go to the MSP tutorials there, and check out sampling tutorial 1:
https://docs.cycling74.com/max8/tutorials/07_samplingchapter01

to summarize a bit: buffer~ is an object that allocates sample-memory for you, and if you want to play back files, you want to load the file into memory, and then use an object like groove~(or play~ or others) to play it back(there is also a simpler object called sfplay~, no buffer~ required, you could check out its helpfile, but seems reverse playback isn't the most straightforward for me to figure out there, haha... i don't use that object much).

to listen to a .wav file from the groove~ helpfile, you could just load the file into buffer~:
go into the helpfile, and edit it so that you simply add a message object attached to the buffer~ which reads, "replace"... when you click on that message to send it to buffer~, buffer~ will open up a file-dialog asking you which file to load into it. after that, because the groove~ object in that helpfile is named similarly to the buffer~ object, groove~ will be able to address the memory space that buffer~ is referring to, thus allowing it to read the samples in the file, and when you send groove~ the '-1' it will then play that file in reverse.

hope that makes sense and helps, if not, the tutorials linked above is the entry-point for most, but nowadays there are also youtube channels that can help, this dude's channel is one of the best:
https://www.youtube.com/user/dude837