We are not lawyers or experts in copyright law! We do not really know what constitutes "fair use" under the law. If songs lyrics are duplicated informally for one-time classroom use or in a slideshow, it is fairly unlikely that you will be prosecuted. Certainly no one is going to be too concerned about single use songsheets typed up for use at a wedding or party. (Although it would be a good idea to at least credit the songwriters and note that the songs on the sheets are copyrighted. It's also a good move to collect the songsheets afterwards and dispose of them.)
On the other hand, many small coffeehouses have been presented with huge bills by organizations like ASCAP for not paying royalties on performances. Catholic dioceses have been prosecuted for including lyrics to songs in the missals used in Sunday AM masses. Churches often have to acquire rights to display lyrics on screens during church conferences.