i want to install a software in redhat enterprise 5. but it says no reo file found. so i want create a repo file in the /etc/yum.repos.d directory. but i don't know what should i write inside the file. can anyone help me !

Use the CentOS repos. Cent is the RHEL source, built for community use. RHEL is really designed to be used with Red Hat support contract (and all the goodies that come along with that), not with yum.

Find more centos repo info here

What is it you want to install ?
post a link to it .

well i have some questions:

1.what does [CentOS5 base] mean? i saw another repo file, where it uses [server]. why? if my pc don't have any internet connection, then what should i write there?

2.what is the purpose of baseurl? is it the url where the installer is?
if i don't have any internet connection what will be my repo file's baseurl?

3.what does 'enable=0' means?

4. if i want to install a software do i have to put the installer inside the /root directory or i can use any directory?

seeing you have redhat enterprise 5. call your already PAID FOR tech support
did you guess
enable=0 means OFF
enable=1 means ON

with out a net connection ,use a computer that has one and by hand download the program you want to install ( AND ALL OF IT'S DEPENDENCIES )
for example if you want to install "the gimp"
not only will you need the program but some of these too as an example
atk.i386 1.20.0-1.fc8
libwmf.i386 0.2.8.4-17.fc8
libpng.i386 2:1.2.29-1.fc8
libXext.i386 1.0.1-4.fc8
libICE.i386 1.0.4-2.fc8
gtkhtml2.i386 2.11.1-2.fc8
libart_lgpl.i386 2.3.19-3.fc8
gnome-vfs2.i386 2.20.0-3.fc
gutenprint-plugin.i386 5.0.2-1.fc8
libtiff.i386 3.8.2-9.fc8
gimp-libs.i386 2:2.4.0-0.rc3.2.fc8
gimp-libs.i386 2:2.4.6-1.fc8
glibc.i386 2.7-2
libpng.i386 2:1.2.29-1.fc8
fontconfig.i386 2.4.2-5.fc8
freetype-freeworld.i386 2.3.5-3.lvn8
freetype.i386 2.3.5-4.fc8
gtk2.i386 2.12.8-2.fc8
gimp-libs.i386 2:2.4.0-0.rc3.2.fc8
gimp-libs.i386 2:2.4.6-1.fc8
libX11.i386 1.1.3-4.fc8
popt.i386 1.13-4.fc8
glib2.i386 2.14.2-1.fc8
glib2.i386 2.14.6-2.fc8
libgnomecanvas.i386 2.20.1-1.fc8
alsa-lib.i386 1.0.16-3.fc8
libmng.i386 1.0.9-5.1
glibc.i386 2.7-2
libXmu.i386 1.0.3-3.fc8
libbonobo.i386 2.20.1-1.fc8
GConf2.i386 2.20.1-1.fc8
dbus-glib.i386 0.73-8.fc8
librsvg2.i386 2.18.2-2.fc8
desktop-file-utils.i386 0.13-3.fc8
poppler.i386 0.6.2-2.fc
libXt.i386 1.0.4-3.fc8
gnome-keyring.i386 2.20.1-3.fc8
gnome-keyring.i386 2.20.3-1.fc8
hicolor-icon-theme.noarch 0.10-2
libXpm.i386 3.5.7-1.fc8
coreutils.i386 6.9-9.fc8
coreutils.i386 6.9-18.fc8
libjpeg.i386 6b-39.fc8
pango.i386 1.18.4-1.fc8
lcms-libs.i386 1.17-5.fc8
zlib.i386 1.2.3-14.fc8

there are no installers .A rpm is just an archive and some scripts .
and double clicking on one should bring up a gui to install it .