Usually you wash the column with some organic, then your mobile phase which will retain your compound. The column support manufacturer of the phase can provide you with a basic guide, which you should review and be trained in, before using.

For help with application specific questions, you can try a keyword search on the web. You should find plenty of papers describing the use of lectins with common affinity supports such as G50. For example: Article Lectin genes and their mature proteins: Still an exciting ma...

Please note that most scientists use a preactivated sephadex material for this purpose, such as GE Healthcare HiTrap™ NHS-Activated HP Columns,

Pierce™ NHS-Activated Agarose Spin Columns, https://www.gbiosciences.com/image/pdfs/protocol/786-1211_protocol.pdf , https://www.purolite.com/dam/jcr:e0554bdd-8db7-4473-a2be-3a7ebe66da96/pre-activated_nhs_brochure.pdf or equivalent brands. You will get a step-by-step protocol with these products.

What do you want to attach to the matrix?

I want to attach D-Galactose to the matrix for the purification of my lectin which is galactose specific @Omar Gonzalez-Ortega

You can use epichlorohydrin or 1,4 butanediol diglycidyl ether at high pH