Installing I2P and first steps
First get the newest version of i2p here. You can choose between 3 different installation types: a graphical installer, headless install and sourcecode. If you use windows or linux with a graphical interface, pick the first one. On headless machines e.g. on rent servers without a monitor choose the headless install. The sourcecode package is only for those, who know what they do.
If you want to, you can also check the files wether something went wrong with the download or they were manipulated. The easiest way is to check the SHA1 hash. Linux users only have to sha1sum i2pinstall_0.*. Compare it with the one that is published on the download page
I2P is completely written in Java (only some crypto-stuff is written in assembler) thus you need a Java RE. Both OpenJRE and Oracle’s will work.
On windows it should do a doubleclick on the i2pinstall-0.xxx.exe and the installation program should start. With linux start the file with
java -jar i2pinstall_0*.exe.